LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

GIFT   OF" 

Mrs.  SARAH  P.  WALS WORTH. 

Received  October,  1894. 
Accessions  No.*?*/         .      Class  No. 


1 


TEBT  I  A  R  Y 

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CRETACEOUS 

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OOLITIC  P*  JURASSIC 


0  N  I  A  N 

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AN 


THE    GEOLOGICAL    EECOED. 

a  represents  the  order  of  deposition  of  the  various  systems  of  the  stratified  rocks  ;  b  the  same 
systems  inclined  at  an  angle,  and  illustrating  the  manner  in  which  the  lower  and  older  systems 
have  been  brought  by  disturbance  to  the  surface  and  made  accessible. — See  Page  17-1,  §179. 


E  L,  L,  S'  S 


FIRST    PRINCIPLES 


OF 


GEOLOGY 


A      TEXT-BOOK 


FOR  SCHOOLS,  ACADEMIES  AND  COLLEGES. 


WITH    OVER  TWO    HUNDRED   ILLUSTRATIONS, 


B  y 


DAVID  A.  ^ELLS,  A.M., 

AUTHOR  OF  "WELLS'S  NATURAL  PHILOSOPHY,"  "PRINCIPLES  AND  APPLICATIONS  OF 

CHEMISTRY,"  "SCIENCE  OF  COMMON  THINGS,"  EDITOR  "ANNUAL  OF 

SCIENTIFIC  DISCOVERY,1'  ETC. 


NEW    Y  O  E  K  : 
IVISON,    PHINNEY,    BLAKEMAN    &   CO., 

CHICAGO:    S.    C.    GEIGGS    &    CO. 

1  864. 


W4 
\ 


Entered,  according  to  Act  of  Congress,  in  the  year  1861,  by 

IVISON,    PHINNEY    &    CO., 

In  the  Clerk's  Office  of  the  District  Court  of  the  United  States  for  the  Southern 
District  of  New  York. 


PREFACE. 

THE  design  of  the  present  work  is  to  furnish  a  text- 
book on  Geology,  adapted  to  the  limited  time  allotted  to 
the  study  of  this  department  of  science  in  the  majority  of 
high-schools,  academies,  and  colleges.  . 

Intimately  connected  as  Geology  is  with  the  great  in- 
dustrial interests  of  the  country — especially  with  mining 
and  agriculture — and  constituting  also  an  important  mem- 
ber of  the  circle  of  the  sciences,  its  place  as  an  element  in 
an  English  educational  course  is  daily  becoming  more  and 
more  recognized.  At  the  same  time,  the  general  educa- 
tional requirement  is,  not  for  minute,  detailed  instruction 
(since  comparatively  few  students  have  either  the  time  or 
inclination  to  render  themselves  experts),  but  rather  for 
the  communication  of  such  general,  comprehensive  views 
of  the  principles  of  Geology  as  shall  prove  most  practically 
useful  to  those  who  propose  to  engage  in  other  than 
scientific  pursuits.  With  this  view,  the  Author,  in  the 
present  work,  has  endeavored  to  avoid  that  elaborate  dis- 
cussion of  facts  and  theories,  and  that  excessive  use  of 
technical  terms  which  render  some  learned  text-books  so 
repulsively  dry  and  wearisome  to  beginners  ;  but,  on  the 
contrary,  without  sacrificing  scientific  exactness  and  com- 
pleteness, has  aimed  to  interest,  as  the  most  efficient  way 
to  instruct. 


VI  PREFACE. 

In  the  preparation  of  the  work,  the  author  lays  no  claim 
to  originality ;  but  he  has  drawn  from  a  multitude  of 
sources  such  material — statements  and  illustrations — as 
has  seemed  most  desirable  for  presentation  to  beginners. 
To  the  elementary  treatises  of  Page  and  Jukes,  (which  at 
present  hold  the  first  place  as  elementary  text-books  on 
geology  in  Great  Britain),  he  is,  however,  especially  in- 
debted' for  many  suggestions.  Great  pains  have  also  been 
taken  to  render  the  work  in  every  respect  correct,  and  in 
full  accordance  with  the  very  latest  results  of  scientific 
research. 

In  conformity  with  the  general  sentiment  of  teachers, 
questions  have  been  appended  to  the  text.  It  is  sug- 
gested, however,  that  the  student  be  not  required  to  com- 
mit to  memory  any  part  of  the  text  verbatim,  but  rather 
that  he  should  make  himse]f  fully  acquainted  with  the 
subject  generally. 

For  further  hints  and  suggestions  relative  to  the  study 
of  Geology,  reference  is  made  to  the  Appendix. 

FEBRUARY,  1861. 


CONTENTS. 


PAGE 

INTRODUCTORY  OUTLINE.  ,,C 9 


CHAPTER    I. 

GENERAL  RELATIONS,  STRUCTURE,  AND  CONSTITUTION  OF  THE  EARTH.  .  .     10 

CHAPTER    II. 

CHEMICAL  AND  MINERALOGICAL  COMPOSITION  OF  ROCKS  .............     1C 


CHAPTER    III. 

ORIGIN  AND  GENERAL  CLASSIFICATION  OF  THE  MATERIALS  CONSTITU- 

TING THE   CRUST  OF  THE   EARTH  ...............................      25 


CHAPTER    IV. 

VARIETIES  AND  LITIIOLOGICAL  CHARACTER  OF  THE  IGNEOUS  ROCKS..  31 

SECTION     I.  —  VOLCANIC  ROCKS  ........  ...................  32 

"         II.—  TRAPPEAN  ROCKS  ............................  36 

"       III.  —  GRANITIC  ROCKS  .......  .  ....................  41 

CHAPTER    V. 

VARIETIES  AND  LITHOLOGICAL  CHARACTERS  OF  THE  AQUEOUS  ROCKS.  .     47 

CHAPTER    VI. 

VARIETIES  AND  LITHOLOGICAL   CHARACTERS   OF  THE  METAMORPHIC 

ROCKS  ..............  •'  '  '  *  Ji  ........  '  .........................     61 

TABULAR  CLASSIFICATION  OF  ROCKS  ..............................     68 

CHAPTER.VII. 

STRUCTURE,  MECHANICAL  DISPLACEMENT,  AND  RELATIONS  o?  ROCKS  .  .     69 


CONTENTS, 


CHAPTER   VIII. 

PAGE 

GEOLOGICAL  AGENCIES.  ...  ......................................  98 

SECTION     I.  —  IGNEOUS  AGENCIES  ..........................  99 

"         II.  —  AQUEOUS  AND  ATMOSPHERIC  AGENCIES  ........  133 

"       III.  —  ORGANIC  AGENCIES  ..........................  160 

"       IV.  —  CHEMICAL  AGENCIES  .........................  166 


CHAPTER    IX. 

CLASSIFICATION  OF  THE  MATERIALS  COMPOSING  THE  EARTH'S  CRUST    * 
INTO  PERIODS,  SYSTEMS,  AND  GROUPS  ..........................  167 


CHAPTER  X. 

PALAEONTOLOGY.  —  GENERAL  CHARACTERISTICS  OF  FOSSILS  ............  180 

CHAPTER    XI. 

HISTORY   OF  THE   FORMATION   OF  THE  SYSTEMS  OF  THE  STRATIFIED 

EOCKS  .....................................................  198 

STRATIFIED  ROCKS  OF  THE  Azoic  PERIOD  .........................  203 

LAURENTIAN  SYSTEM  .....................................  206 

HURONIAN  SYSTEM  .......................................  208 

PALEOZOIC  PERIOD  ........  .....................................  210 

SILURIAN  SYSTEM.  .......................................  210 

DEVONIAN  SYSTEM  .......................................  222 

CARBONIFEROUS  SYSTEM  ...................................  229 

PERMIAN  SYSTEM  ........................................  248 

MESOZOIC  PERIOD  ..............................................  250 

TRIASSIC  SYSTEM  .........................................  250 

OOLITIC,  OR  JURASSIC  SYSTEM  .............................  252 

CHALK,  OR  CRETACEOUS  SYSTEM  ...........................  269 

CAINOZOIC  PERIOD  ....................................  .  ........  278 

TERTIARY  SYSTEM  ...........................  .  ...........  278 

POST-TERTIARY,  OR  RECENT  SYSTEM  .......................  313 

CONCLUSION  ...................................................  322 

APPENDIX..  .  325 


FIRST  PRINCIPLES  OF  GEOLOGY. 


INTRODUCTORY   OUTLINE. 

•1.  Geology  (from  the  Greek  777,  the  earth,  and 
discourse)  is  that  department  of  natural  science  which 
treats  of  the  structure  and  mineral  constitution  of  the 
earth  ;  the  successive  changes  which  have  taken  place  in 
the  organic  and  inorganic  kingdoms  of  nature,  and  the 
agencies  by  which  such  changes  have  been  effected.* 

2.  The  science  of  geology' admits  of  division  into  several  departments,  or 
sub-sciences,  which  are  somewhat  arbitrarily  varied  by  different  writers.  The 
divisions,  however,  most  generally  recognized  and  adopted  for  convenience  of 
study  or  reference,  are  as  follows : — 

(1.)  Descriptive,  or  Phenomenal  Geology ,  which  treats  of j 
the  appearance,  arrangement,  and  physical  condition  of  the  materials  constitut- 
ing the  earth's  structure.  It  embraces,  to  some  extent,  the  same  topics  as 
Physical  Geography. 

*  "  It  is  not  easy  to  give  an  accurate  and  comprehensive  definition  of  the  science  of 
geology.  It  is,  indeed,  not  so  much  one  science,  as  the  application  of  all  the  physical 
sciences  to  the  examination  of  the  structure  of  the  earth,  the  investigation  of  the  processes 
concerned  in  the  production  of  that  structure,  and  the  history  of  their  action.  That  this 
large  view  of  geology  is  not  only  a  true  but  a  necessary  one,  is  shown  by  the  fact,  that 
it  was  not  until  considerable  advances  had  been  made  in  all  the  physical  sciences  which 
relate  directly  to  the  earth,  that  geology  could  begin  to  exist  in  any  worthy  form.  It 
was  not  until  the  chemist  was  able  to  explain  the  nature  of  the  mineral  substances  of 
which  rocks  are  composed ;  not  till  the  geographer  and  meteorologist  had  explored  the 
surface  of  the  earth,  and  taught  us  the  extent  of  land  and  water,  and  the  powers  of 
winds,  currents,  rains,  glaciers,  earthquakes  and  volcanoes  ;  not  until  the  naturalist  had 
classified,  named,  and  described  the  greater  part  of  existing  animals  and  plants,  and  ex- 
plained their  anatomical  structure,  and  the  laws  of  their  distribution  in  space ;— that 
the  geologist  could,  with  any  chance  of  arriving  at  sure  and  definite  results,  commence 
his  researches  into  the  structure  and  composition  of  rocks  and  the  causes  which  pro- 
duced them,  or  .utilize  his  discoveries  of  the  remains  of  animals  and  plants  that  are  in- 
closed in  them.  He  could  not  until  then  discriminate  with  certainty  between  igneous 
and  aqueous  rocks,  between  living  and  extinct  animals,  and  was,  therefore,  unable  to  lay 
down  any  one  of  the  foundations  on  which  his  own  science  was  to  rest." — Encyclopedia 
Britannica,  8th  edition,  vol.  xv. 

1* 


10  FIRST     PRINCIPLES     OF     GEOLOGY. 

(2.)  Dynamical  or  Physical  Geology,  which  considers  the  na- 
ture, action  and  origin  of  the  forces  or  agencies  by  which  the  structure  of  the 
earth  has  been  changed  and  modified. 

(3.)  Paleontology  (from  Tra/laioc,  ancient,  ovra,  beings,  and  Aoyof,  dis- 
course) or  Organic  Geology,  which  restricts  itself  exclusively  to  a  con- 
sideration of  the  remains  of  animals  and  plants  found  imbedded  in  the  rocky 
structure  of  the  earth — their  organization  and  relations  to  the  races  now  liv- 
ing, and  the  laws  which  have  regulated  the  distribution  of  life,  both  in  space 
and  time,  upon  the  surface  of  our  planet. 

(4.)  Practical,  or  Economical  Geology,  which  treats  of  the 
applications  of  geological  science  to  industrial  or  economic  purposes,  such  as 
agriculture,  architecture,  civil  engineering,  mining,  etc. 

3.  Geology  at  one  period  was  regarded  as  a  branch  of 
mineralogy,  but  the  connection  of  the  two  sciences  extends 
only  so  far  as  the  latter  classifies  and  characterizes  a  large 
portion  of  the  objects  employed  by  geology  as  evidence  of 
its  statements. 

Mineralogy  may  be  defined  to  be  that  branch  of  natural 
science  which  treats  of  the  forms,  properties,  chemical  com- 
position and  distribution  of  the  mineral  substances  that 
enter  into  the  constitution  of  the  earth. 

All  terrestrial  matter  that  is  not  animal  or  vegetable,  in- 
cluding air  and  water,  is  regarded  as  mineral. 


CHAPTER    I. 

GENERAL  RELATIONS,  STRUCTURE,  AND  CONSTITUTION  OP 
THE  EARTH. 

4.  Planetary  Relations,— The  earth  is  one  of  the  plan- 
etary bodies  constituting  the  solar  system,  and  performs  an 
annual  revolution  about  the  sun,  at  a  mean  distance  of 
95,000,000  miles,  in  an  orbit  varying  a  little  from  that  of 
a  circle.  It  also  completes  a  revolution  daily,  upon  an 
axis,  which  is  inclined  23°,  27'  to  the  plane  of  its  orbit. 


QCTESTIONS.—  Define  geology?    What  general  divisions  of  the  subject  are  recognized? 
Define  mineralogy?    What  proportion  of  terrestrial  matter  may  be  regarded  as  mineral  ? 


GENERAL  RELATIONS,  ETC.,  OF  THE  EARTH.   11 

A  connection  between  the  planetary  relations  of  the  earth  and  its  external 
geological  structure  may  not  at  first  be  readily  apparent,  but  a  brief  consider- 
ation of  a  few  facts  will  render  this  evident.  For  example,  the  distribution 
of  light  and  heat  and  the  alternation  of  seasons  are  entirely  dependent  upon 
the  distance  of  the  earth  from  the  sun,  upon  the  earth's  periodic  motions,  and 
upon  the  inclination  of  its  axis  of  rotation ;  and  any  change  in  these  condi- 
tions would  occasion  a  change  in  ah1  meteorological  agencies  and  phenomena, 
and  consequently  affect  the  distribution  or  even  continuance  of  animal  and 
vegetable  life ;  furthermore,  a  change  in  the  position  of  the  earth's  axis  of 
rotation  would  necessarily  involve  a  change  in  the  entire  surface  configuration 
of  the  globe,  inasmuch  as  the  present  distribution  of  land  and  sea  would  be 
altered,  as  well  as  the  course  of  all  rivers  and  the  influence  of  the  tides.  In 
fact,  it  has  been  assumed  by  some  authorities  that  changes  of  this  character 
must  be  admitted,  in  order  to  account  satisfactorily  for  the  convulsions  which 
geology  demonstrates  to  have  taken  place  in  past  ages  upon  the  surface  of  our 
planet.* 

5.  Figure  of  the  Earth.— The  form  of  the  earth  is  that 
of  a  sphere,  flattened  at  the  poles — technically,  an  ohlate 
spheroid. 

Measured  from  north  to  south — that  is,  from  pole  to  pole — the  diameter  of 
the  earth  is  7899*1  miles;  while,  measured  from  east  and  west  through  the 
equator,  the  diameter  is  1925-6  miles.  The  equatorial  diameter  thus  exceeds 
the  polar  26'5  miles,  thereby  giving  to  each  hemisphere  a  compression  of 
13^  miles.  This  difference  in  diametrical  measurement  is  more  than  four  times 
the  height  (29,000  feet)  of  the  loftiest  mountain  upon  the  surface  of  the  earth. 

The  form  under  which  atoms  of  matter  group  themselves,  in  obedience  to 
the  law  of  their  mutual  attraction,  and  uninfluenced  by  any  other  force,  is 
always  that  of  a  sphere ;  and  such  must  have  been  the  shape  assumed  by  the 

QUESTIONS.— Is  there  any  connection  between  the  planetary  relations  of  the  earth  and 
its  geological  structure?  "What  is  the  figure  of  the  earth?  What  its  dimensions?  Un- 
der what  circumstances  will  atoms  of  matter  group  themselves  in  the  form  of  a  sphere  ? 


*  The  dependence  of  the  tides,  which  are  among  the  most  permanent  and  important 
agents  concerned  in  producing  geological  changes,  upon  the  attractive  force  of  the  sun 
and  moon  is  universally  admitted ;  but  the  fact  that  all  "  water-power"  (in  the  ordinary 
acceptation  of  the  term)  upon  the  earth's  surface  is,  equally  with  the  tides,  the  result  of 
an  extra  terrestrial  influence,  is  not  so  generally  recognized.  This  will,  however,  be  ob- 
vious, if  we  consider  that  the  momentum,  or  power  acquired  by  water  in  falling  from  a 
higher  to  a  lower  level  through  the  action  of  gravity,  is  the  exact  measure  of  a  force  which 
originally  lifted  the  water  to  the  elevation  from  whence  it  falls,  and  that  this  primary  lift- 
ing power  is  heat  ;— heat  derived  from  the  sun,  which,  in  lines  of  invisible  force,  draws 
up  the  water  as  vapor  from  the  surface  of  the  sea  to  the  height  where,  through  condensa- 
tion, it  becomes  specifically  heavier  than  the  atmosphere,  and  descends  as  rain,  rivulets, 
water-falls,  and  rivers  to  its  original  location.  "  All  the  rivers  run  into  the  sea,  yet  is  not 
the  sea  full ;  unto  the  place  whence  the  rivers  come  thither  they  return  again." 

Numerous  other  facts  of  like  character  might  be  adduced  illustrative  of  the  extent  to 
which  a  connection  can  be  traced,  either  directly  or  indirectly,  between  the  planetary  re- 
lations of  the  earth  and  its  external  geological  structure. 


12         FIRST     PRINCIPLES     OF     GEOLOGY. 

earth  at  the  beginning,  supposing  its  mass  to  have  consisted  of  yielding,  semi- 
fluid materials,  and  provided  it  remained  at  rest  upon  its  axis.  The  moment, 
however,  that  rotation  upon  an  axis  commenced,  its  form  must  have  changed 
from  that  of  a  sphere  to  a  spheroid,  in  virtue  of  the  centrifugal  force  generated, 
which  exerts  itself  at  right  angles  to  the  axis  of  rotation,  and  in  proportion 
to  the  distance  from  that  axis ; — thereby  producing  a  bulging  of  the  earth's 
mass  at  that  part  of  its  surface  where  the  distance  from  the  axis  is  greatest, 
i.  e..  at  the  equator.* 

Although  we  may  not  be  able  to  affirm  positively  that  the  entire  earth  ever 
was  in  a  plastic  or  semi-fluid  condition,  yet,  in  connection  with  certain  geolog- 
ical speculations,  it  is  interesting  to  know  that  its  figure  is  such  as  would 
necessarily  arise  from  the  rotation  of  a  yielding  mass  around  its  own  axis. 

6.  Density  of  the  Earth.— The  mean  density  of  the 
earth  is  at  least  five  times  that  of  waterf  (or  about  one 
half  that  of  silver)  ;  but  the  actual  mean  density  of  the 
rocky  substances  most  common  on  its  surface  is  not  more 
than  half  as  great,  or  about  2 '5.  Hence  the  density  of  the 
earth  increases  from  the  surface  toward  the  center. 

These  facts  have  induced  a  supposition  that  the  earth,  in  its  interior,  must 
be  composed  of  materials  differing  in  composition  or  condition  from  those 
which  make  up  its  external  structure;  since,  with  a  correspondence  through- 
out of  composition,  and  the  law  of  gravitation  acting  uniformly  toward  the 

QUESTIONS. — Under  what  influences  will  a  sphere  become  a  spheroid?  What  is  the 
density  of  the  earth  ? 

*  An  experiment  strikingly  illustrative  of  these  facts  may  be  performed  as  follows : 
oil  will  float  upon  the  surface  of  water,  but  will  sink  to  the  bottom  of  strong  alcohol ;  if, 
therefore,  we  take  a  portion  of  alcohol  in  a  glass  and  drop  into  it  a  globule  of  olive  oil, 
the  spirit  will  float  above,  and  the  oil  will  assume  the  form  of  a  flattened  spheroid.  If 
now  we  add  a  little  water  and  mix  it  carefully  with  the  spirit,  without  breaking  the  float- 
ing mass  of  oij,  it  will  be  seen  to  swim  higher  and  present  less  flatness,  and  by  continuing 
to  carefully  add  water  until  the  mixture  and  the  oil  correspond  in  specific  gravity,  we  may 
at  last  bring  the  globule  to  the  very  center  of  the  fluid,  where,  it  will  assume  the  form  of 
a  perfect  sphere.  If,  under  these  circumstances,  a  slender  wire  is  passed  through  the 
center  of  the  oil  globule  and  rotated,  we  have  immediately  a  flattened  spheroi<|,  which 
will  become  more  so  as  we  increase  the  speed  of  rotation,  until  it  spreads  out  into  a  sheet 
of  oil,  still  held  by  the  revolving  wire.  If  the  rate  of  revolution  is  still  further  increased, 
we  have  a  very  remarkable  result — a  ring  of  oil  separates  from  the  rest,  which,  although 
there  is  no  apparent  connection  between  it  and  its  center,  still  moves  at  a  uniform  rate 
with  it ;  thus  giving  a  miniature  representation  of  the  phenomenon  of  the  ring  of  Saturn. 

t  Distilled  water,  at  a  temperature  of  60"  Fahrenheit,  is  adopted  as  the  standard  of 
comparison. 

The  density  of  the  earth  is  obtained  by  comparing  the  relative  attracting  power  of  par- 
ticular mountains,  or  smaller  masses  of  matter,  with  that  of  the  whole  globe,  and  by 
comparing  the  oscillations  of  a  pendulum  at  the  surface  of  the  earth,  with  those  of  an 
equal  pendulum  at  a  depth  below  the  surface,  as  in  a  mine.  In  this  last  case,  the  differ- 
ence of  the  rates  of  the  two  pendulums  would  indicate  the  different  force  of  gravitation  at 
the  two  positions ;  and  hence  the  density  of  the  earth. 


CKUST     OF     THE     EARTH. 


13 


center,  the  density  of  all  ordinary  rocks,  at  a  very  inconsiderable  depth, 
would,  through  compression,  become  so  great  as  to  give  a  mean  density  to 
the  earth  far  exceeding  that  which  its  astronomical  relations  will  admit  of. 
Thus,  for  example,  it  has  been  calculated  that  air  at  a  depth  of  thirty-four 
miles  from  the  surface  would  become  as  heavy  as  water  ;  water,  at  three  hun- 
dred and  sixty-two  miles,  as  heavy  as  mercury ;  and  that  the  density  of  lime- 
stone (marble)  at  the  center  of  the  earth  would  be  one  hundred  and  nineteen 
times  greater  than  it  is  at  the  surface,  with  but  one  eighth  of  its  ordinary 
bulk.  To  reconcile,  therefore,  the  actual  mean  density  of  the  earth  with  the 
action  of  the  forces  of  attraction  and  gravitation,  it  has  been  suggested  that  the 
condensation  of  the  central  mass  of  the  globe  must  be  counteracted  by  some  ex- 
pansive influence,  such  as  heat,  or  that  it  may  consist  of  matter  as  attenuated  as 
the  lightest  known  gases.  The  appreciable,  or  ponderable  crust  of  the  earth,  how- 
FIG.  1.  ever,  calculating  from  the  astronomical  phenomena 

of  precession  and  nutation,  can  not  be  less  than  a 
fourth  or  fifth  of  the  earth's  radius ;  that  is,  it  can 
not  be  much  less  than  eight  hundred  miles. 

7.  Crust  of  the  Earth, — In  ordinary 
geological    language,   the   expression 
"  crust  of  the  earth"  is  understood  to 
refer  to  that  portion  only  of  the  exte- 
rior of  our  planet  which  is  accessible 
to  human  observation,  or  concerning 
which  we  are  able  to  reason  conclu- 
sively from  observations  made  at  or 
near  the  surface. 

The  thickness  of  such  a  superficial  film  or  en- 
velop is  estimated  by  Lyell  to  be  about  ten  miles, 
or  4-^th  part  of  the  distance  from  the  surface  of 
the  earth  to  the  center.  Other  authorities,  how- 
ever, have  supposed  that  we  can,  by  the  aid  of 
geology,  seo  as  it  were  into  the  interior  of  the 
earth,  as  far  as  twenty  or  even  thirty  miles.  In 
Fig.  1,  a  section  of  the  earth,  a  6,  approximately 
represents  the  superficial  rock  crust,  and  a  d  the 
appreciable  or  ponderable  portion  (required  by  as- 
tronomical calculations)  which  envelops  the  un- 
known interior. 

8.  Surface  Configuration, — The  sur- 
face configuration  of  the  earth,  as  well 

QUESTIONS. — What  inferences  have  been  drawn  from  the  density  of  the  earth  ?  What 
is  understood  by  the  crust  of  the  earth  ?  What  is  the  estimated  thickness  of  the  crust? 
What  is  the  surface  configuration  of  the  earth  ? 

^S 

, 


14         FIRST     PRINCIPLES     OF     GEOLOGY. 

beneath  the  ocean  as  on  the  dry  land,  is  extremely  irregu- 
lar, "being  elevated  into  ridges  and  mountain  chains,  with 
intervening  plains  and  valleys. 

The  mean  height  of  all  the  solid  parts  of  the  earth's  surface  above  the  sea- 
level  has  been  estimated  by  Humboldt  at  about  1,000  feet;  that  of  all  Eu- 
rope, 671  feet;  Asia,  1,132  feet;  South  America,  1,151  feet;  North  America, 
748  feet. 

The  highest  known  mountains  on  the  globe  are  Mounts  Everest  and  Kun- 
chinjinga,  of  the  Himalaya  Eange,  Central  Asia,  which  attain  an  elevation 
respectively  of  29,002  and  28,150  feet  above  the  sea-level.  The  loftiest 
mountain  in  South  America  is  Tupungato,  one  of  the  Chilean  Andes  (22,456 
feet) ;  in  North  America,  Mount  St.  Elias,  one  of  the  Rocky  Mountains, 
17,900  feet,  and  Popocatepetl,  Mexico  (17,884  feet);  in  Europe,  Mont  Blanc 
(15,760  feet).  The  highest  peaks  of  the  Alleghany  or  Appalachian  range, 
which  extends  throughout  the  Atlantic  slope  of  the  United  States,  are  Cling- 
man's  Peak,  Black  mountains,  N.  C.  (6,760  feet) ;  Mount  Washington,  White 
mountains,  N.  H.  (6,285  feet) ;  Tahawas,  or  Mount  Marcy,  Adirondack  mount- 
ains, N.  Y.  (5,467  feet).* 

The  greatest  depth  yet  reached  by  man  in  excavations  does  not  much  ex- 
ceed 2,000  feet  (about  one-third  of  a  geographical  mile)  below  the  level  of  the 
sea.  The  absolute  depth  (i.  e.,  depth  below  the  immediate  surface,)  of  some 
excavations  is,  however,  much  greater.  Thus,  the  mine  of  Kuttenburg,  in 
Bohemia,  which  is  believed  to  be  the  deepest  in  the  world,  has  an  absolute 
depth  of  3,778  feet.  AtMondorff,  in  the  Duchy  of  Luxembourg,  an  Artesian 
well  has  been  bored  to  a  depth  of  2,400  feet  below  the  surface ;  at  Columbus, 
Ohio,  2,340  feet;  at  Louisville,  Ky.,  2,086  feet;  at  Charleston,  S.  C.,  1,145 
feet.  The  deepest  mine  in  America,  viz. :  the  silver  mine  of  Valenciana,  in 
Mexico,  has  an  absolute  depth  of  1,686  feet ;  but  the  bottom  of  this  mine  is 
more  than  5,000  feet  above  the  sea-level 

QUESTIONS.— What  is  the  mean  elevation  of  its  surface  above  the  sea-level  ?  Enume- 
rate the  highast  mountains  ?  What  depth  has  been  reached  by  man  in  artificial  excava- 
tions ? 


*  "  The  inequalities  on  the  earth's  surface,  arising  from  mountains,  valleys,  buildings 
etc.,  have  been  likened  to  the  roughness  on  the  rind  of  an  orange,  compared  with  its  gen- 
eral mass ;  and  the  comparison  is  free  from  exaggeration.  The  highest  mountain  does 
not  much  exceed  five  miles  in  perpendicular  elevation ;  this  is  only  l-1600th  part  of  the 
earth's  diameter.  Consequently,  on  a  globe  of  sixteen  inches  in  diameter,  such  a.  moun- 
tain would  be  represented  by  a  protuberance  of  not  more  than  l-100th  part  of  an  inch, 
which  is  about  the  thickness  of  ordinary  drawing  paper.  Now,  as  there  is  no  entire  con- 
tinent, or  even  any  very  extensive  tract  of  land,  known  where  the  general  elevation  above 
the  sea  is  any  thing  like  half  this  quantity,  it  follows,  that  if  we  would  construct  a  cor- 
rect model  of  our  earth,  with  its  seas,  continents,  and  mountains,  on  a  globe  sixteen  inches 
in  diameter,  the  whole  of  the  land,  with  the  exception  of  a  few  prominent  points  and 
ridges,  must  be  compressed  within  the  thickness  of  thin  writing-paper,  and  the  highest 
hill  would  be  represented  by  the  smallest  visible  grain  of  sand."— SVY  John  Hcrschel 


SURFACE     CONFIGURATION. 


15 


The  depth  of  the  sea  has  been  generally  supposed  to  correspond  with  the 
height  of  the  land.  Soundings,  however,  showing  enormous  depressions  of 
the  ocean-bed,  at  various  points,  have  been  reported,  viz. :  49,800,  46,236,  and 
39,600  feet;  but  the  accuracy  of  them  is  questionable.  According  to  Com- 
mander Maury,  the  average  depth  of  the  Atlantic,  for  a  distance  of  seventy- 
five  to  one  hundred  miles  from  the  coasts  of  continents,  is  less  than  6,000 
feet:  for  a  further  distance  of  from  200  to  300  miles,  the  depth  varies  from 
6,000  to  12,000  feet. 

Fig.  2,  designed  by  Com.  Maury,  U.  S.  1ST.,  represents  the  bed  of  the  At- 
lantic ocean,  as  indicated  by  recent  soundings  and  surveys,  in  a  line  extend- 


loo  go 


ing  southeasterly  from  Mexico  to  Africa.  It  is  drawn  to  a  scale,  and  repre- 
sents the  elevation  of  the  land  above  the  level  of  the  sea,  as  well  as  the  depth 
to  which  the  ocean  sinks  below  it. 

While  the  great  lakes  of  North  America  are  elevated  (one  of  them,  Lake 
Superior,  596  feet)  above  the  ocean,  some  of  the  inland  seas  of  Asia  are  re- 
markably depressed  below  its  level.  Thus,  the  surface  of  the  Caspian  Sea  is 
eighty-three  and  a  half  feet  below  the  level  of  the  Black  Sea ;  that  of  the 
Lake  of  Tiberias,  466  feet  below  the  Mediterranean ;  while  the  surface  of  the 
Dead  Sea  is  1,388  feet  below  the  same,  with  a  depth  of  water,  in  some  places, 
of  300  fathoms  (1,800  feet).  Fig.  3  represents  the  respective  levels  of  the 
Mediterranean  and  Dead  Sea,  with  that  of  the  adjacent  country. 

9.  Distribution  of   Land   and   Water,— The  surface  of 
the  earth  has  been  estimated  to  contain  about  196,800,000 

QUESTION. —What  is  known  respecting  the  depth  of  the  sea  ?  What  is  said  of  the  ele- 
vation and  depression  of  the  beds  of  lakes  ?  What  is  the  area  of  the  earth's  surface 


16         FIKST     PRINCIPLES     OF     GEOLOGY. 

square  miles.     Of  this  area  the  dry  land  is  supposed  to  oc- 
cupy about  51,500,000  square  miles,  leaving  the  remainder 

FIG.  3. 


of  the  surface,  145,300,000  square  miles,  covered  with 
water  ;  or  the  distribution  of  land  and  water  is  in  the  pro- 
portion of  1  to  2-84. 


CHAPTER    II. 

CHEMICAL  AND  MINERALOG-ICAL  COMPOSITION  OF  ROCKS. 

10.  Rock, — Popularly  the  term  "  rock"  is  applied  only  to 
the  more  compact  and  solid  portions  of  the  globe  ;  but, 
used  in  a  geological  sense,  it  includes,  not  merely  mineral 
masses  which  are  hard  and  consolidated,  as  granite,  lime- 
stone, etc.,  but  also  all  natural  accumulations  of  looser 
and  less  coherent  materials,  such  as  beds  of  sand,  clay, 
gravel,  etc. 

11.  Chemical  Composition  of  Rocks,— Chemistry  has  es- 
tablished the  existence  of  sixty-two  *  distinct  forms  or 
modifications  of  matter,  each  of  which  must,  in  relation  to 
'the  present  state  of  our  knowledge,  be  considered  as  a 

"simple,"  or  "elementary"  substance.f     Of  these,  but 

QUESTIONS. — What  is  said  of  the  distribution  of  land  and  -water  ?    In  what  sense  does 
the  geologist  use  the  term  rock  ?     What  is  tho  number  of  the  recognized  elements  ? 


*  Sixty-five,  according  to  some  authorities. 

t  The  term  "  wndecomposed,"  in  place  of  "  elementary,"  better  conveys  the  idea  en- 
tertained  by  modern  chemists  in  respect  to  these  substances. 


COMPOSITION     OF     ROCKS.  17 

comparatively  few  enter  into  the  composition  of  the  crust 
of  the  globe,  while  many  are  so  exceedingly  rare  that  they 
are  known  only  to  chemists. 

The  names  of  the  elementary  substances  which  constitute  the  great  mass 
of  all  the  rocks,  consolidated  or  unconsolidated,  which  are  accessible  to  man, 
are  as  follows ; — 

12.  Non-Metallic  Elements,  —  OXYGEN,  HYDROGEN, 
CHLORINE,  CARBON,  SULPHUR,  PHOSPHORUS,  and  SILI- 
CON— 7. 

Metals  of  the  Alkalies  and  Earths,— POTASSIUM,  SO- 
DIUM, CALCIUM,  MAGNESIUM,  and  ALUMINUM — 5. 

Metals  Proper , — IRON  and  MANGANESE — 2.    Total  14. 
Of  these,  two  only,  carbon  and  sulphur,  are  found  pure 
as  minerals  ;  the  rest  occur  only  in  combination. 

Oxygen  is  the  most  abundant  of  all  the  elementary  substances.  It  consti- 
tutes at  least  one  third  part  of  the  solid  crust  of  the  globe,  and  eight-ninths, 
by  weight,  of  all  the  water  upon  its  surface.* 

Hydrogen,  as  a  constituent  of  water,  enters  into  the  composition  of  many 
minerals  and  mineral  strata,  and  forms  part  of  almost  every  organic  substance. 
Chlorine  is  abundantly  present  in  common  salt  (chloride  of  sodium)  of  which 
it  forms  nearly  seven-twelfths  by  weight :  it  also  occurs  in  many  other  com- 
binations. 

Carbon  is  found  pure  in  the  diamond ;  is  the  chief  constituent  of  all  varieties 
of  coal  and  of  graphite  (plumbago,  black-lead),  and,  as  an  element  of  carbonic 
acid,  forms  nearly  one-eighth  part  of  carbonate  of  lime,  (ordinary  limestone 
and  marble). 

Sulphur  occurs  native  as  a  volcanic  product,  and,  in  combination  with  a 
large  number  of  metals,  forming  sulphurets  (sulphides) ;  in  an  oxydized  con- 
dition, as  sulphuric  acid,  it  is  still  more  widely  diffused  in  combination  with 
various  earths,  as  the  sulphates  of  lime,  magnesia,  baryta,  etc.  Nearly  one 
third  of  the  weight  of  sulphate  of  lime  (gypsum,  or  plaster  of  Paris)  is  sulphur. 
Phosphorus  exists  in  small  quantities,  but  widely  diffused,  in  the  mineral 
kingdom,  principally  in  combination  with  lime. 

Silicon,  in  combination  with  oxygen  forming  silica,  or  silicic  acid,  is  the 

QTTESTIONS. — How  many  constitute  the  great  mass  of  the  rocks  ?    Enumerate  them  ? 


*  One  point  in  this  connection  is  especially  worthy  of  notice,  as  bearing  on  the  impor- 
tant question  of  the  former  condition  of  our  globe,  namely,  that  about  one  half  of  all  the 
ponderable  matter  of  the  earth's  crust,  taking  into  consideration  oxygen,  hydrogen,  and  car- 
bonic acid,  is  capable  of  existing,  or  maybe  said  to  exist  naturally,  in  a  gaseous  condition. 


18          FIRST     PRINCIPLES     OF     GEOLOGY. 

most  abundant  of  all  solid  substances,  and  has  been  estimated  to  form  forty- 
five  per  cent,  of  all  the  ponderable  matter  of  the  globe. 

Aluminum,  the  metallic  base  of  the  earth  alumina,  is  the  characteristic  con- 
stituent of  all  clays,  and  is  also  present  in  almost  all  other  rocks.  Alumina 
has  been  estimated  to  form  ten  per  cent,  of  the  crust  of  the  globe. 

Potassium,  sodium,  and  magnesium,  the  metallic  bases  from  whence  are 
derived  the  salts  of  potash,  soda,  and  magnesia,  are  also  very  widely  dissemi- 
nated. Sodium,,  united  with  chlorine,  forms  common  salt;  and  magnesia, 
beside  constituting  an  important  part  of  some  rocks,  is  an  abundant  constitu- 
ent of  sea-water. 

Calcium,  in  combination  with  oxygen,  forms  the  well-known  mineral  lime, 
which,  in  turn,  united  with  carbonic  acid,  as  carbonate  of  lime  (ordinary  lime- 
stone, marble),  is  estimated  to  constitute  one  seventh  of  the  crust  of  the 
globe.  Lime  and  magnesia  are  also  diffused  almost  universally  throughout 
the  silicious  rocks,  in  the  form  of  sDicates  of  lime  and  magnesia. 

Of  the  metals,  commonly  so  called,  iron  and  manganese  are  the  most  widely 
diffused  (as  oxyds)  j  and  the  former  has  been  calculated  to  form  at  least  two 
per  cent,  of  the  crust  of  the  globe. 

In  addition  to  the  above-named  elementary  substances, 
fluorine,  iodine,  gold,  arsenic,  and  titanium  may  also  be 
mentioned  as  having  a  very  general  distribution,  but  in 
very  minute  quantities. 

13.  General   Mineralogical   Composition   of   Rocks, — 
Nearly  all  the  minerals  which  make  up  the  great  rock- 
masses  constituting  the  crust  of  the  globe  have  resulted 
from  the  chemical  combination  of  two  or  more  of  the  above 
enumerated  simple  substances.     Most  of  the  common  min- 
erals, furthermore,  may  be  characterized  as  being  either 
silicious  or  calcareous. 

14.  Silicious  Minerals  are  those  in  which  silica  (silex, 
or  silicic  acid)  predominates. 

This  substance,  as  a  constituent  of  rocks,  occurs  under  two  forms,  viz.,  as 
a  pure  or  simple  mineral,  and  as  an  acid  united  to  mineral  bases.  When 
pure,  or  merely  colored  by  small  quantities  of  different  metallic  oxyds,  it  is 
generally  termed  "  quartz,"  and  as  such  occurs  in  amorphous,  massive  rock- 
masses,  or  veins — common  quartz,  and  in  crystals — crystallized  quartz.  The 
prevalent  color  of  common  quartz  is  white — often  milk-white  or  gray ;  when 
pure,  or  nearly  so,  it  is  translucent,  with  a  vitreous  or  glassy  luster.  It  may 
have,  however,  almost  every  shade  of  color,  and  even  a  granular  texture. 

QUESTIONS.— What  is  said  of  their  distribution  and  combinations?  What  is  the  general 
mineralogical  composition  of  rocks  ?  What  minerals  arc  termed  silicious  ?  What  are  the 
principal  forms  of  silica  ? 


COMPOSITION     OF     ROCKS. 


19 


PIG.  4 


Crystallized  quartz,  when  transparent  and  colorless,  is  termed  rock-crystal 
The  fundamental  form  of  quartz  crystals  is  a  regular  six-sided  prism,  ter- 
minated by  six-sided  pyramids  ;  (See  Fig.  4.)  perfect  specimens  of  this 
form,  however,  are  rare,  and  the  crystals  usually  met  with  are  modifications 
of  it.  Amethyst  is  quartz  coloied  purple  by  the 
presence  of  oxyd  of  manganese.  Agate  is  a  gen- 
eral name  given  to  a  semi-pellucid,  uncrystallized 
variety  of  quartz,  presenting  various  tints  in  the 
same  specimen,  the  colors  being  deh'cately  arranged 
in  stripes  or  bands,  or  blended  in  clouds.  "When 
the  colors  and  bands  are  not  very  numerous,  but 
are  arranged  in  flat,  horizontal  layers,  the  speci- 
men is  termed  an  Onyx ;  and  when  the  colors  are 
mixed  irregularly,  they  are  called  "  Moss-agates." 
Agate  of  a  pearly  or  smoky-gray  color,  is  called 
Chalcedony',  and  specimens  presenting  a  blood- 
red  color,  either  uniformly  distributed  or  in  patches,  are  termed  carnelians, 
and  are  much  used  in  the  less  expensive  kinds  of  jewelery.  Jasper  is  the 
name  given  to  highly  compact,  opaque  varieties  of  quartz  colored  by  iron ; 
they  admit  of  a  high  polish,  and  often  present  zones,  or  bands  of  color  like 
agates.  Flint  is  a  massive,  compact  variety  of  Silica,  of  a  gray,  brown,  or 
black  color:  its  fracture  is  conchoidal,  and  it  is  often  found  in  masses  of 
grotesque  and  irregular  shape.  Buhrstone  (mill-stone)  is  a  variety  of  cellular 
flint,  well  adapted  for  grinding.  Opal,  crysoprase,  and  lloodstone,  are  other 
varieties  of  nearly  pure  silica.  Common  sand  is  usually  composed  of  grains  of 
silica ;  its  ordinary  yellow  or  brown  color  being  due  to  the  presence  of  oxyd 
of  iron,  or  of  organic  matter.  Sandstone  is  an  aggregate  of  such  grains 
cemented  into  a  coherent  mass. 

"When  silica  plays  the  part  of  an  acid  and  unites  with  other  minerals,  the 
resulting  compounds  are  termed  silicates.  If  we  except  carbonate  and  sul- 
phate of  lime,  carbonate  of  magnesia,  quartz,  and  coal,  nearly  all  the  mineral 
constituents  of  the  great  rock-masses  of  the  globe  are  silicates. 

Pure  day  is  a  hydrated*  silicate  of  alumina,  but  as 
commonly  found,  (common  clay),  it  contains  in  addition 
variable  proportions  of  silica  (sand),  iron,  lime,  magnesia, 
carbon,  and  the  alkalies. 

Any  very  finely  divided  mineral  matter,  however,  which  contains  from  ten 
to  thirty  per  cent,  of  alumina,  and  is  consequently  "plastic,"  or  capable  of 
retaining  its  shape  on  being  molded  or  pressed,  would  be  usually  called  clay. 

Rocks  and  minerals  which  contain  a  notable  percentage  of  alumina  or  clay 

QTTESTIONS. — What  arc  silicates?    What  is  the  composition  of  clay? 


Hydrated — containing  a  proportion  of  water  in  chemical  combination. 


20          FIRST     PRINCIPLES     OF     GEOLOGY. 

emit,  when  breathed  upon,  a  peculiar  and  distinctive  odor  (argillaceous  odor), 
which  is  easily  recognized. 

Clays  which  are  nearly  free  from  oxyd  of  iron,  carbonate  of  lime,  or  the 
alkalies,  are  termed  "fire-clays,"  and  being  almost  infusible,  are  used  for  the 
manufacture  of  fire-bricks,  crucibles,  etc.  Sach  clays,  however,  are  compar- 
atively rare  and  valuable. 

Pure  silica  is  one  of  the  most  infusible  substances  with  which  we  are  ac- 
quainted. 

Glass  and  porcelain  are  examples  of  artificial  silicates  (i.  e.,  of  potassa,  soda, 
lime,  alumina  or  iron) ;  but  for  the  production  of  these  compounds  the  most 
intense  furnace  heab  is  requisite,  a  fact  which  it  is  well  to  bear  in  mind  when 
speculating  on  the  origin  and  formation  of  certain  rocks. 

Highly  silicious  rocks  and  minerals  may  be  recognized 
by  their  hardness,  infusibility,  and  insolubility  in  ordinary 
acids.  Quartz  strikes  fire  with  steel,  is  not  scratched  with 
a  knife,  but  readily  scratches  glass  and  most  other  sub- 
stances, except  a  few  gems. 

15.  Calcareous  Minerals  are  those  in  which  lime  pre- 
dominates. 

As  a  constituent  of  mineral  masses,  lime  generally  occurs,  united  with  car- 
bonic acid,  as  a  carbonate,  and  in  this  condition  it  exhibits  a  great  diversity 
of  structure  and  appearance.  The  principal  modifications  of  carbonate  of 
lime,  however,  are  the  following:  chalk;  earthy,  granular,  compact,  and  con- 
cretionary limestones;  crystalline  limestones,  or  crystalline  marbles,  and  calca- 
reous marls.  Carbonate  of  lime  is  also  the  principal  constituent  of  the  hard 
parts  of  corals,  shells,  etc.,  and  consequently  of  the  rock-masses  formed  of  the 
remains  of  these  organisms. 

Any  rock  which  contains  at  least  half  its  weight  of  carbonate  of  lime  may 
be  properly  termed  a  limestone ;  and  the  presence  of  other  mineral  matters 
commingled  with  the  carbonate  of  lime  is  generally  indicated  by  giving  to  the 
limestone  a  distinctive  name.  Thus,  we  have  argillaceous  (clayey)  limestone ; 
silicious ;  magnesian  (containing  magnesia) ;  ferruginous  (containing  iron)  ; 
bituminous ;  or,  from  the  presence  and  decomposition  of  organic  matter,  fetid 
limestone. 

The  term  marble  is  applied  to  those  varieties  of  compact  and  crystalline 
limestones  which  are  capable  of  being  worked  in  all  directions,  and  also  of 
taking  a  good  polish.  It  is  an  architectural  rather  than  a  geological  term. 

QUESTIONS. — What  characteristic  have  aluminous  rocks  and  minerals  ?  When  are  clays 
available  for  fire-clays?  What  are  examples  of  artificial  silicates?  What  are  the  char- 
acteristic properties  of  highly  silicious  rocks  ?  When  are  rocks  and  minerals  termed 
calcareous  ?  In  what  condition  is  lime  found  most  abundantly  ?  What  are  the  principal 
modifications  of  carbonate  of  lime  ?  When  may  a  rock  be  termed  limestone  ?  What  is 
marble  ? 


COMPOSITION     OF     ROCKS.  21 

Limestones  which  contain  twenty  per  cent,  and  upward  of  carbonate  of 
magnesia  are  called  magnesian  limestones;  granular  and  crystalline  varieties 
of  magnesian  limestone  are  termed  Dolomite  (from  an  eminent  French  geol- 
ogist, Dolomieu). 

Oolite  (Gr.  uov,  an  egg,  and  /U0of,  a  stone)  is  the  name  applied  to  lime- 
stones made  up  more  or  less  completely  of  small  rounded  particles  like  the 
eggs  or  roe  of  a  fish  (whence  the  name).* 

Limestones,  especially  the  marbles,  exhibit  every  variety  and  shade  of 
color — the  coloring  agents  being,  for  the  most  part,  metallic  oxyds,  and  es- 
pecially the  oxyd  of  iron.  Black  limestones  and  marbles,  however,  owe  their 
color,  in  great  part,  to  the  presence  of  carbonaceous  matter,  derived  from 
the  decomposition  of  animal  or  vegetable  matter  originally  contained  in  the 
rock :  when  subjected  to  intense  heat  they  become  white. 

Carbonate  of  lime  is  found  in  a  greater  variety  of 
crystalline  forms  than  any  other  known  substance.  Its 
primary  form  is  a  rhombohedron,  as  seen  in  "  double 
refracting,"  or  "  Iceland  spar"f  (see  Fig.  5) ;  but  of  this 
figure  over  650  modifications  are  known  to  mineralogists. 
The  crystalline  structure  of  limestone  in  rock-masses  is 
best  displayed  in  that  variety  of  marble  known  as  "  statu- 
ary marble."  Crystalized  carbonate  of  lime  is  very  often  spoken  of  as  "  calc- 
spar,"  (i.  e.j  cafcareous  spar.) 

The  presence  of  carbonate  of  lime  in  a  rock  may  be  ascertained  by  applying 
to  the  surface  a  drop  of  any  dilute  acid  (as  sulphuric  acid,  or  even  vinegar), 
which  has  a  stronger  affinity  for  lime  than  carbonic  acid  has ;  the  latter,  being 
thus  liberated,  escapes  in  a  gaseous  form,  and  causes  an  effervescence  in  the 
drop  of  liquid. 

Lime  also  occurs  somewhat  abundantly  in  nature  in  combination  with  sul- 
phuric acid,  forming  sulphate  of  lime,  or  gypsum,  and  with  silicic  acid  form- 
ing silicate  of  lime.  Sulphate  of  lime  may  be  distinguished  from  carbonate 
of  lime  by  its  softness,  and  by  the  absence  of  effervescence  on  the  applica- 
tion of  acids. 

16.  Specific  Mineral  Constituents  of  Rocks, — Consid- 
ered specifically,  the  composition  of  the  great  rock-masses 
which  constitute  the  crust  of  the  globe  is  represented  by 
an  extremely  small  number  of  simple  minerals — some  eight 

QUESTIONS.— What  are  magnesian  limestones  and  dolomites  ?  What  is  oolite  ?  What 
is  said  of  the  color  of  limestones  ?  What  of  the  crystalline  forms  of  carbonate  of  lime  ? 
How  may  the  presence  of  carbonate  of  lime  in  a  rock  be  ascertained  ? 


*  Oolites,  or  oolitic  limestones,  although  common  in  the  geological  formations  of  Eu- 
rope, are  rarely  met  with  in  the  United  States. 

t  The  term  "  spar"  is  applied  in  mineralogy  to  those  crystals  or  minerals  which  break 
up  into  rhombs,  cubes,  plates,  prisms,  etc.,  with  smooth,  plane  faces.  Hence  we  have 
calc-spar,  fel-spar,  brown-spar,  etc. 


22 


FIRST     PRINCIPLES     OF     GEOLOGY. 


or  nine — which  are  repeated  over  and  over  again  in  the 
different  formations.  They  are,  1,  quartz  ;  2,  feldspar  ; 
'3,  mica  ;  4,  hornblende  ;  5,  augite  ;  6,  carbonate  of  lime  ; 
7}  talc  ;  8,  serpentine  ;  9;  oxydof  iron.* 

As  it  is  difficult  to  convey  fully  to  the  mind,  by  •written  descriptions,  tho 
physical  characters  of  minerals,  it  is  recommended  to  the  student  to  obtain 
accurately-named  specimens  of  the  above-enumerated  species,  and  to  render 
himself  thoroughly  conversant  with  all  their  modifications — their  characters 
in  rock-masses  being  often  very  obscure.  The  following  descriptions  may, 
however,  assist  in  their  recognition. 

Quartzite  is  a  term  applied  to  granular  varieties  of  quartz,  and  to  sand- 
stones apparently  converted  by  heat  or  chemical  solvents  into  quartz. 

Feldspar,  as  chiefly  composed  of  silica,  alumina,  and  potassa,  is  a  softer 
mineral  than  quartz.  It  is  found  crystalline,  generally  of  a  reddish-Vhite,  or 
gray-color,  with  a  vitreous  luster  inclining  to  pearly.  The  softer  crystals  oc- 
curring in  granite  are  of  feldspar,  and  admit  of  being  scratched  with  a  knife, 
when  the  quartz,  from  its  extreme  hardness,  receives  no  impression.  Feld- 
spar crystals  may  be  also  recognized  by  the  smooth,  glassy  aspect  of  their 
divisional  planes.  \ 

Mica.  This  mineral  (so  called  from  the  Latin  mico,  I  glisten)  is  distinguished 
by  its  brilliant,  semi-metallic  luster,  and  its  ready  division  into  extremely  thin 
plates,  or  laminse,|  which  are  transparent  or  translucent,  flexible  and  elastic. 

QUESTIONS.— What  are  the  principal  minerals  that  make  up  the  great  rock-masses  of 
the  globe  ?  What  is  quartzite  ?  What  is  feldspar  ?  Mica  ? 


*  The  average  composition  of  these  minerals  is  represented  in  the  following  tahie : 


MINERAL  SPECIES. 

Quartz, 
when 

-* 

Feld- 
spar, 

common 

Mica. 

Horn- 
blonde. 

Augite. 

Talc. 

Carbon- 
ate of 
lime, 
pure. 

Serpen- 
tine. 

Oiyd 

of  iron, 
pure. 

Silica 

100-00 

65-52 

48-00 

4027 

55-32 

62-61 

4370 

17-61 

34-25 

16-36 

0-43 

2-76 

.  .    ... 

0-94 

0-13 

13-80 

23-01 

55-93 

0'42 

13-38 

16-99 

32-51 

39-96 

"  * 

12-98 

8-75 

...... 

0-29 

***** 

Soda 

1-70 

1-98 

0'80 

4'  50 

15'34 

2-16 

10-03 

100-00 

Oxyd  of  manganese  . 

0-50 

1-59 

090 

43-58 

Water  

1-25 

0-46 

4-83 

Fluorine  ... 



0-29 

0-57 

t  The  term  "  feldspar"  properly  applies  to  a  group  of  allied  minerals  rather  than  to  a 
single  species.  This  group  includes  the  following  varieties:  1,  common,  or  ordinary 
feldspar,  in  which  the  alkali  is  potash ;  2,  albite  or  soda-feldspar,  in  which  the  potash  is 
replaced  by  soda ;  and  3,  "  Labradorite,"  or  "  Labrador  feldspar,"  in  which  both  soda 
and  lime  replace  the  potash.  The  last  also  differs  from  the  two  former  in  often  having  an 
irridescent  appearance,  and  in  its  manner  of  fracture  and  cleavage. 

\  Mica  is  sometimes  used  as  a  substitute  for  glass  (i.  e.,  in  furnace  doors,  etc.)  and  ac- 
cording to  Hauy  is  divisible  into  laminse  only  1 -25,000th  of  an  inch  thick. 


COMPOSITION     OF     KOCKS.  23 

It  is  always  present  in  true  granite ;  is  the  principal  constituent  of  a  set  of 
slaty  rocks  called  mica-schists,  or  slates,  and  occurs  also  in  minute  scales  in 
many  sandstones,  imparting  to  them  a  silvery  appearance. 

Hornblende,  so  named  from  its  horny,  glistening  fracture  (also  from  the  Ger- 
man bknden,  to  dazzle),  is  a  black,  or  dark-green  mineral,  softer  than  quartz 
or  feldspar,  and  an  abundant  constituent  of  the  massive  crystalline  rocks.  It 
occurs  massive,  as  hornblende  rock,  or  with  a  slaty  structure,  as  hornblende 
slate  or  schist. 

Augite  (pyroxene)  is  a  blackish-green  or  greenish-gray  mineral,  allied  to 
hornblende,  but  differing  somewhat  in  crystalline  form  and  chemical  compo- 
sition. It  is  the  characteristic  mineral  constituent  of  rocks  of  an  undoubted 
igneous  origin,  as  trap,  basalt,  lava. 

Talc  is  a  very  soft  mineral,  of  a  greenish  color,  a  pearly  luster  and  unctuous 
"  feel."  When  pure,  it  occurs  usually  in  foliated  masses,  easily  separable  into 
thin,  translucent  plates,  which  are  flexible  but  not  elastic,  a  characteristic 
which  especially  distinguishes  it  from  mica.  Talc  is  a  silicate  of  magnesia, 
and  enters  largely  into  the  composition  of  a  variety  of  slaty  rocks  called  "  tal- 
cose."  Steatite  (Gr.  crreap,  fat,  or  suet)  is  a  compact  variety  of  talc.  From  its 
greasy  or  soapy  feel,  it  is  also  known  as  "  soapstone,"  although  this  peculiar- 
ity belongs  to  most  rocks  which  contain  a  considerable  percentage  of  magne- 
sia. "French  chalk,"  "pot-stone,"  and  "Rensselaerite,"  are  varieties  of 
steatite. 

Chlorite  is  a  greenish  mineral,  a  silicate  of  magnesia  and  alumina,  somewhat 
resembling  talc. 

Serpentine  is  a  hydrated  silicate  of  magnesia,  with  varying  proportions  of 
iron,  manganese,  alumina,  lime,  and  sometimes  chromium.  It  is  generally  of 
a  variegated  green  color,  and  derives  its  name  from  the  resemblance  of  its 
mottled  colors  to  the  skin  of  a  serpent. 

Oxyd  of  iron  is  present,  in  greater  or  less  quantity,  in  almost  all  rocks,  and 
often  imparts  to  the  minerals  containing  it  a  red,  brown,  or  yellow  color.  It 
is  the  coloring  agent  of  the  red  and  brown  sandstones.*  Oxyd  of  iron  also 
constitutes  rock-masses,  and  sometimes  entire  mountains,  as  the  "Iron- 
mountain"  of  Missouri. 


QUESTIONS.— "What  is  hornblende  ?  Augite?  Talc?  Chlorite?  Serpentine?  What 
is  said  of  the  distribution  of  oxyd  of  iron  ?  Are  rocks  in  general  made  up  of  distinct 
mineral  species  ? 


*  Bricks  and  common  pottery-ware  owe  their  red  color  to  the  iron  naturally  contained 
in  the  clay  of  which  they  are  formed — the  iron,  by  the  action  of  heat,  being  converted 
into  the  red  oxyd  of  iron.  Some  varieties  of  clay,  like  that  found  near  Milwaukie,  Wis., 
contain  little  or  no  iron,  and  the  bricks  made  from  it  are  consequently  of  light  yellow 
color. 

The  presence  of  iron  in  almost  all  rocks  can  be  demonstrated  by  pulverizing  a  frag- 
ment, digesting  it  in  weak  hydrochloric  or  sulphuric  acid,  and  adding  to  the  filtered  so- 
lution, diluted,  a  drop  of  solution  of  ferrocyanide  of  potash  (yellow  prussiate  of  potash)  ; 
if  the  most  minute  quantity  of  iron  is  present,  the  solution  will  immediately  assume  a 
beautiful  blue  color. 


24         FIRST     PRINCIPLES     OF     GEOLOGY. 

A  few  of  these  minerals  exist  in  a  separate  state,  in  so  large  masses  as  to 
be  denominated  "rock;"  as  quartz,  carbonate  of  lime,  serpentine,  etc.;  but,  in 
general,  the  most  common  rocks  are  formed  by  the  union  of  from  two  to  four  of 
them ;  as  granite,  for  example,  which  is  formed  bj  the  union  of  quartz,  mica 
and  feldspar.  In  rocks  which  have  resulted  from  deposition,  as  sediment  in 
water  (sedimentary  or  stratified  rocks),  the  simple  minerals  which  enter  into 
their  composition  are  generally  so  much  ground  down  and  comminuted  pre- 
vious to  their  final  deposition  and  consolidation,  that  the  mass  appears  entirely 
homogeneous,  as  hi  the  shales,  slates,  etc. 

Other  minerals  forming  rocks  of  small  extent,  or  entering  so  largely  into 
the  composition  of  rocks  as  to  modify  their  character,  are  the  following : — 
sulphate  of  lime  (gypsum),  chloride  of  sodium  (common  salt),  coal,  bitumen, 
garnet,  schorl,  staurotide,  epidote,  pyrites  (sulphuret  of  iron). 

Water  also  constitutes  a  part  of  nearly  all  rocks ;  but  in  most  cases  its 
presence  is  simply  mechanical,  and  is  not  essential  to  the  chemical  composi- 
tion of  the  mineral  substance.  In  a  few  minerals,  however,  it  is  an  abundant 
chemical  constituent,  forming  nearly  twenty  per  cent,  of  sulphate  of  lime, 
twelve  of  serpentine  and  chlorite,  and  three  or  four  of  talc.  A  compound 
containing  water  in  definite  proportions  is  termed  a  hydrate ;  while  a  sub- 
stance entirely  free  from  water  in  combination  is  said  to  be  anhydrous.* 


CHAPTER    III. 

ORIGIN  AND  GENERAL  CLASSIFICATION  OP  THE   MATERIALS 
CONSTITUTING-  THE  CRUST  OF  THE  EARTH. 

17.  ALL  the  rocks  which  make  up  the  crust  of  the  globe 
may,  by  reason  of  certain  structural  peculiarities,  or  by 
reference  to  differences  in  their  mode  of  origin  or  formation, 
be  divided  into  a  few  great  general  groups  or  classes. 

A  classification  founded  on  differences  in  structural  ar- 
rangement, and  one  that  is  most  easily  and  generally  recog- 
^    nized,  divides  all  rocks  into  two  classes,  viz.,  STRATIFIED 
and  UNSTRATIFIED  EOGKS. 

QUESTIONS. — What  minerals,  other  than  those  enumerated  are  found  abundantly  ? 
To  what  extent  does  water  enter  into  the  composition  of  rocks  ?  What  is  a  hydrate  f 
When  is  a  substance  said  to  be  anhydrous  ?  How  are  rocks  classified  ?  What  two  classes 
are  generally  recognized  ? 


*  "  The  presence  of  water  in  rocks  is  known  by  experience ,  since  no  stone  is  ever 
quarried  which  will  not  part  with  some  water  on  being  dried,  either  naturally  in  the  air, 
or  artificially."— Jukes. 


CRUST     OF     THE     EARTH. 


25 


*  < 

18.  Stratified  Rocks, — Kocks  are  said  to  be  stratified 
when  they  are  completely  and  naturally  divided,  by  nearly 
parallel  planes,  into  beds  or  layers.  (See  Fig.  6.)  These 
layers  are  technically  termed  strata  (plural  of  the  Latin 
stratum,  strewn  or  spread  out),  and  may  vary  in  thickness 
from  the  fraction  of  an  inch  to  many  feet. 

FIG.  G. 


Masses  or  layers  of  one  variety  of  rock,  occuring  in  the  midst  of  other 
strata,  are  said  to  be  interstratified. 

Lamination, — The  same  structure,  which  characterizes 
the  stratified  rocks  in  mass,  may,  in  most  instances,  be  ob- 
served in  degree  in  each  separate  bed  or  stratum  of  the 
mass  j  inasmuch  as  the  materials  which  enter  into  their 
composition  are  generally  arranged 
in  thin  layers  or  lamina?,  which  may 
or  may  not  be  separable  from  each 
other.  Such  a  structural  arrange- 
ment is  termed  lamination. 

Fig.  7  represents  some  of  the  forms  of  lami- 


FIG.  7. 


nation — waved,  fine  and  coarse — observable  in  different  strata. 


QUESTIONS.—  When  arc  rocks  said  to  be  stratified  ?    What  is  lamination  ? 

2 


26 


FIRST     PRINCIPLES     OF     GEOLOGY 


Stratified  rocks  are  estimated  to  occupy  about  nine-tenths  of  all  the  land 
surface  of  the  earth. 

19.  Unstratified  Rocks, — Bocks  which  do  not  exhibit 
in  their  structure  any  divisional  arrangement  of  strata  and 

laminae,  are  called 
unstratified.  Such 
rocks  have,  in  gen- 


FIG. 8. 


eral,  an 


exceedingl 


irregular,  massive  ap- 
pearance. (See  Fig. 
8.)* 

20.  Another  classification, 
generally  recognized,  and  by 
many  geologists  preferred  to 
any  other,  is  founded  on  the 
mode  in  which  rocks  have  apparently  originated. 

That  different  rocks  have  had  an  entirely  diverse  origin  must  be  obvious  to 
even  the  most  superficial  observer  .  but  the  fact  will  appear  more  especially 
manifest  if  \ve  minutely  examine  and  compare  well-characterized  specimens 
of  the  most  common  varieties. 

Thus  in  specimens  selected  generally  from  the  class  of  unstratified  rocks 
(as  granite,  trap,  or  porphyry,  for  example),  the  particles  of  mineral  matter 
which  make  up  the  mass  are  internally  compact,  mutually  imbedded  or  inter- 
laced, and  very  often  present  a  crystalline  structure  throughout ;  or  else  con- 
tain distinct,  isolated  crystals  imbedded  in  a  homogeneous  mass.  When 
broken,  they  tend  to  separate  into  irregular  angular  fragments.  Now,  it  is 
a  law  of  physics  that  matter  can  only  assume  a  crystalline  form  when  its  par- 
ticles are  free  to  move  and  arrange  themselves ;  and  hence,  whenever  we  find 
a  crystal  or  a  mineral  particle  that  has  a'n  internal  crystalline  structure,  we 
may  feel  assured  that  it  has  at  some  time  been  in  a  fluid,  or  nearly  fluid  con- 
dition ;  or,  in  other  words,  that  it  has  been  either  dissolved  or  melted.  And 
if  this  conclusion  be  true  as  regards  individual  crystals  or  particles,  it  must 
be  also  true  of  rocks  which  are  made  up  of  such  crystals  or  particles. 


QUESTIONS.— What  is  said  of  the  distribution  of  the  stratified  rocks  ?  When  are  rocks 
termed  unstratified  ?  What  is  said  of  the  origin  of  rocks  ?  What  peculiarity  of  struc- 
ture do  some  rock  specimens  present  ?  "What  does  the  existence  of  a  crystalline  structure 
in  minerals  indicate  ? 

•  The  teacher  or  student,  even  if  without  access  to  a  geological  cabinet,  will  experience 
no  difficulty  in  obtaining  specimens  of  these  two  classes  of  rocks ;  granite,  greenstone, 
and  porphyry  being  illustrative  of  the  unstratified  rocks,  and  slates  and  sandstones  of  the 
stratified.  Opportunity  also  should  be  taken  by  the  learner  to  examine  the  character- 
istics of  these  rocks  in  place,  or  natural  position. 


CRUST     OF     THE     EARTH.  .27 

Rocks  may,  however,  present  evidence  of  former  fluidity  or  plasticity  other 
than  that  afforded  by  the  existence  of  a  crystalline  structure.  Some  do  not 
differ  materially  in  appearance  from  the  products  artificially  formed  in  blast- 
furnaces, being  compact  and  vitreous  (glassy),  or  even  porous  and  slag-like ; 
while  others  seem  to  have  been  deposited  in  shapeless  masses  from  solutions 
in  water. 

These  considerations,  therefore,  have  induced  geologists 
to  ascribe  to  many  rocks  a  chemical  origin,  and  also  to  di- 
vide rocks  thus  originating  into  two  classes,  viz.,  IGNEOUS 
KOCKS,  or  those  which,  in  accordance  with  chemical  laws, 
have  consolidated  from  fusion  ;  and  AQUEOUS  KOCKS,  or 
those  which,  under  similar  laws,  have  been  deposited  from 
solution. 

21.  If,  however,  we  examine  specimens  of  oilier  varieties  of  rocks,  we 
shall  find  that  the  mineral  particles  which  enter  into  their  composition, 
whether  internally  crystalline  or  internally  compact,  are  not  mutually  im- 
bedded and  interlaced  like  those  of  the  chemically  formed  rocks,  but  have 
evidently  been  brought  together  from  different  places,  and  adhere  to  each 
other  in  consequence  of  having  been  forced  together  by  mechanical  pressure, 
or  because  they  are  cemented  together  by  some  other  substance.  In  rocks 
of  this  character,  moreover,  the  particles  are  usually  arranged  in  layers  or 
strata,  and  are  generally  more  or  less  rounded  and  smoothed  externally,  as  if 
water- worn ; — this  latter  appearance,  in  some  instances,  being  especially  ob- 
vious, inasmuch  as  the  whole  mass  of  the  rock  consists  of  pebbles  or  rounded 
fragments  of  other  rocks,  cemented  in  sand,  which  is  also  the  result  of  an 
abrading  process.  In  other  cases,  as,  for  example,  in  many  slates,  sandstones 
and  limestones,  the  constituent  particles  of  the  successive  layers  appear  to 
have  been  deposited  as  mud,  and  are  too  much  comminuted  to  be  separately 
discernible  oven  with  the  aid  of  a  lens. 

From  these  considerations,  therefore,  it  is  evident  that 
the  origin  of  rocks  thus  constituted  was  mechanical  ;  or, 
in  other  words,  the  materials  of  which  they  are  composed 
have  been  derived  from  other  and  older  rocks,  and  have 
been  transported  to  their  present  sites  mainly  through  the 
agency  of  currents  of  water  :  while  their  characteristic  ar- 
rangement into  layers  or  strata  is  obviously  the  result  of 


QUESTIONS.— What  other  evidence  is  there  of  former  fluidity  or  plasticity  of  mineral 
matter?  Into  what  two  classes  may  rocks  of  a  chemical  origin  be  divided?  What  is 
said  of  the  structure  of  other  varieties  .of  rocks?  What  is  the  assumed  origin  of  such 
rocks? 


28 


FIRST      PRINCIPLES     OF     GEOLOGY 


their  having  been  strewed  out  in  succession  over  the  bot- 
tom of  the  lakes  and  seas  in  which  they  were  deposited. 
They  have  hence  been  called  SEDIMENTARY  or  AQUEOUS- 
MECHANICAL  ROCKS,  and  very  generally,  also,  in  allusion 
to  their  structural  arrangement,  STRATIFIED  BOCKS. 

That  the  view  entertained  by  geologists  respecting  the  origin  of  the  above- 
described  rocks  is  correct,  is  further  shown  by  the  fact  that  earthy  deposits 
characterized  by  the  same  horizontally  of  arrangement  and  the  same  water- 
worn  form  of  their  particles,  are  continually  in  the  process  of  formation  near 
the  mouths  of  rivers  or  on  the  land  during  temporary  inundations ;  for  when- 
ever a  running  stream  charged  with  mud  and  sand  has  its  velocity  checked, 
as  when  it  enters  a  lake  or  sea,  or  overflows  a  plain,  the  sediment  previously 
held  in  suspension  by  the  motion  of  the  water  sinks  by  its  own  gravity  to  the 
bottom,  the  heavier  particles  first,  while  the  finely  comminuted  matter  settles 
more  gradually,  and  is  often  floated  to  a  great  distance.*  In  this  way  layers 
of  gravel,  mud  and  sand,  constituting  strata,  are  thrown  down  upon  one 

FIG.  9. 


another,  as  is  represented  in  Fig.  9.f  The  same  arrangement  of  sediment 
may  also  be  observed  in  the  dry  bed  of  almost  every  pond,  and  even  in  little 
pools  formed  by  a  shower. 

22.  Fossiliferous  and  Unfossilifcrous  Rocks,— Rocks, 
according  as  they  are  characterized  by  the  presence  or  ab- 
sence of  fossils,  are  further  distinguished  as  FOSSILIFEROUS 
and  UNFOSSILIFEROUS. 

Fossil, — Any  organic  substance,  the  remains  or  product 

QUESTIONS.— How  have  they  been  designated  ?  What  evidence  is  there  that  the  as- 
sumed sedimentary  origin  of  such  rocks  is  correct  ?  How  may  rocks  be  characterized  by 
the  presence  or  absence  of  fossils  ?  What  is  a  fossil? 


*  The  sediment  brought  down  by  the  Amazon  discolors  the  waters  of  the  ocean  at  a 
distance  of  three  hundred  miles  from  its  mouth  ;  while  much  of  that  discharged  by  the 
Mississippi  into  the  Gulf  of  Mexico  is  swept  by  the  Gulf  stream  into  the  Atlantic. 

t  "  The  annual  floods  of  the  Nile  in  Egypt  are  well  known,  and  the  fertile  deposits  of 
mud  which  they  leave  on  the  plains.  This  mud  is  stratified,  the  thin  layer  thrown  down 
in  one  season  differing  slightly  in  color  from  that  of  a  previous  year,  and  being  separable 
from  it."— LyelL 


CRUST     OF     THE     EARTH.  29 

of  an  animal  or  plant,  imbedded  in  the  earth  by  natural' 
causes,  or  any  recognizable  impression  or  trace  of  such  a 
substance,  is  called  "  a  fossil"  (Latin  fossus,  dug  up). 

In  many  instances  the  fossil  remains  of  animals  and  plants  occur  in  such 
abundance  as  to  constitute  almost  the  entire  mass  of  some  rocks  : — immense 
masses  of  limestone,  for  example,  appearing  oftentimes  to  bo  wholly  composed 
of  shells  or  corals  mineralized  and  cemented  together ;  while  coal,  in  all  its 
varieties,  is  believed  to  bo  entirely  the  product  of  an  extinct  vegetation. 

23.  Me  tarn  orphic  Rocks. — In  addition  to  those  varieties 
of  rocks  which  present  marked  evidence  of  a  distinctive 
igneous  or  aqueous  origin,  geologists  recognize  a  third  great 
class,  which  appear  to  have  originated  from  other  rocks  by 
alteration.  Rocks  of  this  character  are  hence  termed 
METAMORPHIC,  or,  literally,  transformed  rocks  (Gr.  juera, 
change,  jwop</>?J,  form). 

Metamorphic  rocks  are  usually  more  or  less  indurated  and  crystalline,  con- 
tain few  or  no  traces  of  fossils,  and  for  the  most  part  exhibit  stratification  ; 
although  this  structure  in  them  is  often  indistinct  and  sometimes  entirely  ob- 
literated. The  general  theory  of  their  origin  is,  that  their  constituent  mate- 
rials were  originally  deposited  from  water  as  sediment,  but  subsequently, 
through  the  action  of  heat,  pressure,  chemical  solvents,  or  other  agencies, 
were  changed  and  altered.  In  some  cases,  where  sedimentary  strata  contain- 
ing fossils  aro  in  contact  with  rocks  of  undoubted  igneous  origin,  the  whole 
process  of  change  (metamorphosis)  can  bo  clearly  traced  ;' — dark  limestones, 
replete  with  shells  and  corals,  for  example,  being  converted  into  white  crys- 
talline marbles  with  every  sign  of  an  organic  body  completely  obliterated. 

Among  the  common  rocks  which  are  regarded  as  unmistakably  metam  or- 
phic,  may  be  mentioned  those  known  as  the  crystalline  limestones  (statuary 
marble),  "  indurated  clay."  or  "roofing  slate;"  and  gneiss,  which  last  resem- 
bles (and  is  popularly  called)  granite. 


24.  Recapitulation,— From  the  above  considerations  we 
may  class  all  the  rocks  which  constitute  the  crust  of  the 
globe  as  follows  : — 

According  to  tlicir  structural  arrangement  into  STRATI- 
FIED AND  UNSTRATIFIED  EOCKS. 


QTTESTIOXS. — What  arc  raetamorphic  rocks  ?    What  is  the  assumed  origin  of  the  meta- 
morphic  rocks  ? 


30  FIRST     PRINCIPLES     OF     GEOLOGY. 

According  to  the  presence  or  absence  of  organic  re- 
mains, into  FOSSILIFEROUS  AND  UNFOSSILIFEROUS  ROCKS. 

And,  according  to  their  origin  or  mode  of  j  or  mat  ion., 
into  IGNEOUS,  AQUEOUS  and  METAMORPHIC 

The  student,  however,  would  do  well  to  bear  in  mind  that  all  classifications 
of  this  character  are  in  the  highest  degree  general,  inasmuch  as  rocks  of 
every  variety  may  so  intermingle  and  insensibly  graduate  into  one  another  as 
to  render  it  extremely  difficult  to  decide  what  agency  was  most  concerned  in 
their  formation.  And  it  has  not  unfrequently  happened  in  the  history  of 
geological  science  that  rocks  which  have  been  pronounced  by  good  observers 
to  belong  to  one  class,  have,  when  subsequently  seen  under  different  circum- 
stances, or  when  examined  more  thoroughly,  been  referred  to  an  altogether 
different  class. 

Adopting  the  classification  of  Igneous,  Aqueous  and  Metamorphie  in  the 
present  work,  as  most  in  accordance  with  the  established  facts  of  geology  and 
chemistry,  and  most  convenient  for  reference  and  study,  we  may  indicate  tho 
characteristic  features  of  each  division  as  follows : — 

"  The  Igneous  Rocks  are  almost  entirely  chemically 
formed  rocks,  but  some  of  their  varieties  may  have  me- 
chanical accompaniments."  They  are  unstra  tilled  and  un- 
fossiliferous. 

"  The  Aqueous  Rocks  are  either  chemical,  mechanical, 
or  organic  ;  those  of  mechanical  origin  being  by  far  the 
most  abundant."  They  are  for  the  most  part  stratified 
and  fossiliferous. 

The  Metamorphie  Rocks  are  all  more  or  less  changed  and 
altered.  In  some  the  original  structure  and  composition 
are  still  obvious  ;  while  in  others  they  are  entirely  ob- 
scured, or  even  replaced  by  entirely  different  characters. 

25.  Formation, — The  term. formation  is  applied  in  geol- 
ogy to  any  portions  of  the  earth's  crust,  of  greater  or  less 
thickness,  which  were  formed  under  the  same  contempo- 
rary influence. 

A  formation  may  include  rocks  of  very  diverse  character  and  composi- 
tion, when  there  is  reason  to  suppose  that  they  originated  at  nearly  the  samo 

QUESTIONS. — Do  rocks  admit  of  a  precise  and  definite  classification?  Give  the  charac- 
teristic features  of  the  igneous,  aqueous  and  metamorphic  rocks.  What  is  a  formation  in 
geology ? 


IGNEOUS     ROCKS.  31 

epoch.     Thus  we  speak  of  stratified  and  unstratified,  fresh-water  and  marine, 
aqueous  and  volcanic,  carboniferous  (coal-bearing)  and  motaliferous  formations. 


CHAPTER    IV. 

VARIETIES  AND  LITHOLOGICAL  CHARACTERS  OF  THE 
IGNEOUS  ROCKS. 

26.  BY  the  lithological  characters  of  rocks  we  under- 
stand their   external   aspect,  mineralogical   composition, 
texture/""  and  such  other  physical  features  as  can  be  deter- 
mined by  the  inspection  of  hand  specimens. 

27.  Three  classes  of  rocks,  formed  mainly  by  the  action 
of  heat,  are  recognized  by  geologists,  viz.;  the  VOLCANIC, 
TRAPPEAN,  and  GRANITIC. 

According  to  such  a  classification,  the  term  Volcanic  is 
applied  exclusively  to  the  products  of  modern  volcanoes, 
or  to  rocks  formed  through  igneous  agency  within  a  com- 
paratively recent  period,  at  or  near  the  surface  of  the  earth. 
The  terms  Trappean  and  Granitic,  on  the  other  hand,  are 
applied  to  classes  of  igneous  rocks  much  older  than  the 
volcanic,  and  which  are  generally  believed  to  have  con- 
solidated below  the  immediate  surface  of  the  earth,  and 
consequently  under  pressure. 

The  Trappean  and  Granitic  rocks,  in  reference  to  their  supposed  origin, 
have  been  also  called  Plutonic,  from  Pluto,  the  ruler  of  the  inferior  regions. 

28.  Kocks  of  igneous  origin,  with  few  exceptions,  are 
composed  of  minerals  which  are  silicates.      These  min- 
erals are  mainly  silicates  of  alumina,  of  magnesia,  and  of 

QUESTIONS.— What  is  understood  by  the  lithological  characters  of  rocks?  Into  what 
classes  have  the  igneous  rocks  been  divided  ?  What  is  said  of  the  structure  and  chemi- 
cal composition  of  the  igneous  rocks  ? 


*  The  structure  of  a  rock  refers  to  the  manner  in  which  it  occurs  in  mass ;  its  texture, 
on  the  contrary,  refers  to  the  manner  in  which  its  individual  particles  are  internally  ar- 
ranged. Thus,  granite  has  a  massive  structure  ;  but  its  texture  is  crystalline,  coarse  or 
fine  grained,  hard  and  compact. 


32          FIRST     PRINCIPLES     OF     GEOLOGY. 

lime,  with  admixtures  of  silicates  of  potash,  soda,  iron  and 
manganese. 

The  varieties  of  the  mineral  feldspar  (silicate  of  alumina  and  potassa)  consti- 
tute the  basis  of  most  igneous  rocks  ;  those  iii  which  no  feldspar  of  any  kind  is 
present  being  very  few  and  unimportant,  even- if  they  exist  at  all.  After 
feldspar  the  varieties  of  hornblende  and  augite  (silicates  of  magnesia  and  lime) 
hold  the  next  most  important  place. 

Igneous  rocks  exhibit  great  diversities  of  texture  ;  some  being  crystalline 
and  granular,  others  compact  and  stony,  and  Others  glassy  or  vitreous.  These 
differences  are  generally  referred  to  the  diversity  of  circumstances  under 
whicli  the  rocks  in  question  have  consolidated  rather  than  to  differences  in 
their  chemical  composition ;  similar  transformations  being  observed  to  take 
place  in  masses  of  silicates  artificially  fused  (as  in  the  manufacture  of  glass) 
and  cooled  under  different  conditions. 

The  terms  "  unstratified,"  "  Plutonic,"  and  "  pyrogenous"  are  often  used  by 
geologists  in  describing  rocks  which  have  been  formed  by  the  action  of  heat, 
as  synonymous  with  the  term  igneous. 

SECTION    I. 

VOLCANIC     R  0  C  K  S . 

29.  The  volcanic  rocks  are  the  only  igneous  rocks  whose' 
formation  we  are  at  present  able  to  witness. 

In  one  sense,  all  the  strictly  igneous  rocks  are  volcanic ;  that  is,  they  have 
been  formed  through  the  agency  of  heat,  in  a  manner  similar  to  the  pro- 
ducts of  existing  volcanoes.  For  the  sake  of  classification,  however,  the  use 
of  the  term  is  restricted  by  geologists  to  those  rocks  which  have  been  formed 
by  the  action  of  heat  within  a  comparatively  recent  period,  at  or  near  the  sur- 
face of  the  earth,  in  air,  or  in  water. 

A  volcano  (from  Vulcanus,  the  God  of  fire)  is  an  open- 
ing in  the  crust  of  the  earth,  from  whence  melted  or  heated 
rock,  ashes,  water,  smoke,  gases  or  vapors  are  discharged. 

A  volcano  is  usually  a  more  or  less  perfectly  conical  hill  or  mountain,  with 
a  truncated  apex,  produced  by  the  successive  accumulations  of  ejected  matter 
or  by  the  elevation  of  a  portion  of  the  earth's  crust.  The  vent  or  opening 
communicating  with  the  interior  of  the  earth  (which  in  tho  first  instance 

QUESTION'S. — What  are  the  principal  minerals  which  enter  into  their  composition  ? 
What  is  said  of  the  texture  of  the  igneous  rocks?  What  is  the  origin  of  the  diversities 
of  texture  exhibited  ?  What  synonyms  for  the  term  "  igneous'1  are  often  used  ?  What 
peculiarity  characterizes  the  volcanic  rocks  ?  To  what  rocks  is  the  term  volcanic  re- 
stricted ?  What  is  a  volcano  ? 


CRUST     OF      THE     EARTH. 


33 


must  have  been  merely  a  fissure)  in  such  cases  assumes  tho  form  of  an  in- 
verted cone,  and  is  called  a  cra'er.  Volcanic  cones  vary  in  height  from  90 
feet,  to  23,900  feet  (Aconcagua,  Chili.)  ' 

A  volcanic  fissure  or  orifice  which  emits  only  smoke, 
gases,  aqueous  and  corrosive  vapors,  is  termed  a  SOLFA- 

TARA  Or  FUMAROLE. 

When  volcanoes  exist  beneath  the  sea,  as  they  not  un- 
frequently  do,  they  are  termed  sub-aqueous  or  sub-marine. 
Those  which  have  exhibited  no  evidence  of  action  since  the 
commencement  of  the  historic  period  are  termed  extinct, 
while  those  which  are  constantly  or  intermittingly  in  action 
are  termed  active-. 

FIG.  10. 


The  general  name  given  to  all  melted  rock  matter  ejected 
from  volcanoes  is  lava. 

Fig.  10  represents  an  ideal  section  of  a  volcano  during  an  eruption ;  a  13 


QUESTIONS.— What  is  a  solfatara?    When  are  volcanoes  said  to  be  sub-marine?    When 
active  and  extinct?   What  is  lava  ? 

2* 


34         FIRST     PRINCIPLES      OF     GEOLOGY. 

the  volcanic  fissure,  or  channel,  communicating  with  the  interior  of  the  earth 
filled  with  lava ;  &,  the  crater ;  c,  the  volcanic  cloud  of  srnoke  and  vapor 
above  the  crater;  d,  the  spheroidal  shape  assumed  by  the  smoke  column  ;  e, 
the  shower  of  lava  or  dust  falling  from  the  volcanic  cloud ;  f,  falling  scorioe 
and  ashes ;  g,  lateral  channel  discharging  lava  at  a  point  below  tho  crater ;  i, 
lava  stream,  with  smoke  issing  from  fumaroles. 

30.  Tho  mineral  constituents  of  almost  all  volcanic  rocks 
or  lavas  are  mainly  feldspar  and  augite.  When  the  feld- 
spar predominates  the  lavas  are  termed  tra-cliyte  or  fel- 
spathic  lavas  ;  and  when  the  augite  is  in  excess,  augitic 
lavas. 

The  trachytes  are  so  called  from  the  Greek  word  rpo^^f,  rough,  as  they 
have  commonly  a  rough,  gritty  feel  to  the  finger. 

Lavas  assume  nearly  every  variety  of  texture  and  color,  according  to  tho 
varying  proportions  of  feldspar  and  augite  which  enter  into  their  composi- 
tion, and  according  to  the  slowness  or  rapidity  with  which  the  mass  is  cooled ; 
— those  which  have  cooled  quickly  being  compact  and  glassy,  while  those 
which  have  cooled  slowly  and  under  pressure,  tend  to  become  stony  and 
crystalline.  Some  varieties  of  trachyte  at  first  sight  resemble  granite. 

Obsidian,  or  volcanic  glass,  is  the  vitreous  condition  of  a  lava.  It  is  of 
various  shades  of  color,  often  velvet  black,  and  can  scarcely  be  distinguished 
from  the  product  of  a  glass  furnace.  It  was  formerly  used  by  tho  ancients  as 
a  material  for  mirrors.  Pumice  is  the  solidified  froth  or  scum  of  molten  rock 
matter ;  it  has  a  pearly  silky  luster,  a  fibrous  texture,  and  is  often  sufficiently 
light  to  float  upon  water.  It  is  generally  of  a  grayish-white  color,  and  is 
extensively  used  as  polishing  material. 

Scoriae,  is  the  name  given  to  all  accumulations  of  dust,  ashes,  cinders  and 
slaggy  rock  fragments  discharged  from  volcanoes.  Vokanic  tufa,  or  tuff(iis\\) 
is  the  general  name  given  to  volcanic  rocks  of  a  soft,  earthy  and  porous 
texture ;  it  ordinarily  consists  of  ashes  and  dust,  mixed,  it  may  be,  with 
coarser  fragments,  blown  from  a  volcanic  focus.  Materials  of  this  character 
falling  upon  the  land  may  become  compacted  into  rock  either  by  the  pressure 
of  their  own  weight,  or  in  consequence  of  tho  percolation  of  water  containing 
mineral  matter  in  solution  ;  if,  on  the  contrarj-,  they  fall  into  the  sea,  they 
become  subjected  to  the  conditions  under  which  all  other  mechanically  formed 
aqueous  rocks  are  produced,  and  may  exhibit  stratification  and  contain 
fossils.* 

Among  other  substances  occasionally  ejected  from  volcanoes  are  fragments 

< 

QUESTIONS. — What  are  the  principal  mineral  constituents  of  lava  ?  What  two  classes 
of  lavas  are  recognized?  What  is  said  of  the  texture  of  lavas?  What  is  obsidian? 
What  is  pumice '?  What  are  scoria}  ?  What  are  volcanic  tufas  ? 


*  The  word  "  tuff,"   or  "  tufa,"  used  alone,  may  signify  any  porous,  vesicular  rock  ; 
thus  we  say  "calcareous-tufa,"  "trap-tufa,"  "volcanic  tufa,"  etc. 


VOLCANIC     PRODUCTS.  35 

of  granite  or  other  rocks,  scarcely  altered ;  also  sulphur  in  a  pure  state ; 
chlorides  of  sodium  (common  salt),  potassium,  iron,  lead,  copper,  sulphate  of 
lime  (gypsum),  sal-ammoniac,  borax  (borate  of  soda). 

"  Volcanic  mud,  which  bubbles  out  of  many  fissures  and  openings  (known 
as  mud  volcanoes),  is  a  product  of  considerable  magnitude  in  some  regions ; 
and  jets  of  hot  water  (like  the  geysers  of  Iceland)  and  those  of  steam  (like 
the  suffoni  of  Italy)  are  not  unfrequent  volcanic  phenomena." 

The  principal  gaseous  emanations  of  volcanoes  are  carbonic  acid,  sulphur- 
etted hydrogen,  sulphurous  acid,  hydrochloric  acid,  and  sometimes  carbu- 
retted  hydrogen. 

31.  The  products  described  in  the  preceding  paragraphs  may  be  found,  to 
a  greater  or  less  extent,  in  almost  all  volcanic  districts ;  and  the  m'ode  in 
which  they  are  discharged,  their  varying  admixtures,  and  the  different  ap- 
pearances they  assume,  according  to  the  rapidity  or  slowness  with  which 
they  have  cooled,  afford  highly  instructive  lessons  to  the  geologist.     Here  the 
explosive  force  of  highly  heated  vapors  and  molten  matter  breaks  through  the 
solid  crust  of  the  earth,  and  uplifts  or  deranges  rocks  of  anterior  formation ; 
there  the  lava  penetrates  every  fissure,  or  issuing  from  some  vent  flows 
down  the  mountahi  side,   filling  up  valleys,   damming  up  river  channels, 
creating  crags  and  cliffs,  and  spreading  over  plains ;  hero  scorias  and  ashes 
are  showered  forth,  borne  abroad  by  the  winds,  and  scattered  over  land  and 
sea,  sometimes  burying  cities  and  villages,  as  in  the  case  of  Pompeii  and 
Herculaneum ;  there  heated  vapors  are  perpetually  exhaling  from  rents  and 
fissures,  and  incrustirig  their  sides  with  mineral  or  metallic  compounds.    Re- 
peated discharges  from  volcanic  vents  may  give  rise  in  time  to  mountains ; 
or  taking  place  under  water,  may  be  spread  out  over  the  bed  of  the  ocean,  aitd 
become  overlaid  by  true  sediments — thus  producing  alternations  of  igneous 
nnd  aqueous  rocks.     The  molten  matter  also  cools  unequally — here  forming 
vitreous  masses  (obsidian),  there  porous  pumice  or  rough  earthy  tufa ;  here 
granular  trachytes,  there  highly  compact  crystalline  rocks.     And  just  as  ig- 
neous forces  are  acting  at  the  present  day  under  the  eye  of  the  observer,  in 
the  production  of  volcanic  rocks,  so  it  is  inferred  they  have  acted  in  former 
ages  of  the  world  in  the  production  of  other  varieties  of  igneous  rocks  (the 
trappean  and  granitic) :  with  this  difference,  that  many  of  the  latter  have 
been  formed  at  great  depths  and  under  great  pressure,  and  have  subsequently 
undergone  internal  changes  to  which  volcanic  or  sub-aerial  igneous  rocks  have 
not  been  subjected. — PAGE. 

32.  Surface  Con  figu  ration  ofVolcanic  Districts . — In  dis- 
tricts where  volcanic  eruptions  have  been  frequent,  and  where  the  surface  has 
not  been  exposed  to  great  aqueous  denudation,  cones  and  craters,  with  vast 
beds  of  scoriaceous  lavas  and  volcanic  sands  constitute  the  marked  features  of 


QUESTIONS. — What  are  occasional  volcanic  products  ?  What. are  the  principal  gaseous 
emanations  of  volcanoes  ?  What  inferences  and  lessons  do  existing  volcanic  phenomena 
afford  to  geologists  ?  What  is  said  of  the  surface  configuration  of  volcanic  districts  ? 


36          FIRST     PRINCIPLES     OF     GEOLOGY. 

the  scenery.     Fig.  11  represents  a  view  of  a  chain  of  extinct  volcanic  lulls 
in  Auvergnc,  Central  France. 

FIG.  11. 


33.  Geographical  Distribution  .—In  the  United  States,  east  of 
the  Rocky  Mountains,  volcanic  rocks  do  not  occur ;  but  throughout  this  whole 
chain  of  mountains,  and  especially  in  its  continuations,  as  the  Cordilleras  of 
Mexico  and  the  Andes  of  South  America,  volcanic  formations  are  abundant. 
They  also  occur  in  the  "West  Indies,  the  Cape  de  Verde  and  Canary  Islands, 
in  France,  Germany,  Italy,  in  many  districts  of  Asia,  and  in  numerous  islands 
of  the  Pacific  and  of  the  Polar  Oceans.     In  the  British  Islands  they  are  un- 
known.   • 

34.  Industrial   P  r  o  d  u  c  t  s .—  In  an  industrial  point  of  view,  volcanic 
products  are  of  considerable  importance.    Nearly  all  the  sulphur  of  commerce  is 
derived  from  volcanic  districts,  Sicily  alone  yielding  nearly  100,000  tons  yearly. 
Sulphur  occurs  in  Sicily  in  beds  of  blue  clay,  and  the  excavations,  in  some 
instances,  resemble  quarries  of  yellow  marble.     Pumice  is  extensively  used  in 
the  arts  for  dressing,leather  and  for  polishing  and  smoothing  wood,  metals, 
glass  and  marble.     Large  quantities  of  it  are  annually  exported  from  the 
Lipari  Islands,    Mediterranean,  the  price  being  from  $30  to  $50  per  ton, 
according  to  the  quality.     Borax  (boracic  acid  and  soda)  may  also  be  regarded 
as  a  volcanic  product — the  principal  supply  being  afforded  by  the  hot  springs 
(lagoons)  pf  Tuscany,  which  yield  about  1,000  tons  of  crystallized  boracic  acid 
annually.     Borax  is  also  found  in  the  waters  of  some  of  the  hot  springs  of 
California.     Volcanic  rocks  rarely  contain  available  deposits  of  the  metals, 
but  yigld  many  interesting  simple  minerals,  more  than  one  hundred  different 
species  having  been  noted  among  the  lavas  of  Vesuvius  alone ;  the  propor- 
tion which,  they  constitute  of  the  whole  mass,  however,  is  inconsiderable. 

SECTION     II. 

TRAPPEAN   ROCKS. 

35.  The  term  "  trap"  (from  the  Swedish   "  trappa"  a 
stair)  was  originally  applied  to  certain  igneous  rocks,  which, 

QTTESTIONS.—  What  of  the  distribution  of  volcanic  rocks?    "What  of  the  industrial  pro. 
ducts  of  volcanoes  ?     What  is  the  origin  and  application  of  the  term  "  trap?" 


TBAPPEAN     ROCKS.  37 

occurring  in  great  tabular  masses  of  unequal  extent,  give 
to  many  hills  a  terraced  or  step-like  appearance. 

At  present,  however,  the  terms  "  trap"  and  "  trappean" 
are  used  somewhat  indefinitely  and  vaguely  by  geologists 
to  designate  any  igneous  rock  which  cannot  be  said  to  be 
distinctly  granitic  on  the  one  hand,  or  absolutely  volcanic 
on  the  other. 

36.  In  texture  and  composition  the  trap-rocks  are  extremely  diversified 
and  varied — some  being  highly  crystalline  and  compact,  while  others  aro 
cellular  or  soft  and  earthy.  Their  relations  to  the  other  rocks  are  also  often 
intricate  and  deceptive.  Sometimes  they  present  themselves,  as  already 
stated,  in  tabular  masses,  which  are  not  divided  into  strata;  sometimes  in 
shapeless  heaps  and  irregular  cones,  forming  chains  of  small  hills ;  and  very 
often,  as  veins  or  wall-like  masses,  they  burst  through  and  intersect  rocks  of 
every  description,  deranging  their  position  and  spreading  over  them  in  sheets 
of  varied  extent  and  thickness.  Trap-rocks  are  also  frequently  found  divided 
into  columns  of  great  regularity.  The  annexed  figure  represents  a  very 
characteristic  appearance  of  trap  bluffs  or  exposures. 


3t.  Mineralogically  considered,  the  trap- rocks  are  chiefly  composed  of  feld- 
spar, hornblende  and  augite,  with  varying  admixtures  of  oiivine  (a  greenish 
mineral,  a  silicate  of  magnesia  and  iron),  quartz,  clay,  iron,  etc.  Their 
weathered  and  decomposing  surfaces,  owing  to  the  presence  of  oxyd  of  iron, 
are  generally  of  a  rusty  brown  color. 

38.  In  structure  and  arrangement  the  trap-rocks  exhibit 
unmistakable  evidence  of  igneous  origin,  and  in  a  majority 

QTTESTIONS.—  What  is  said  of  the  structure  and  composition  of  the  trap-rocks  ?  What 
of  their  mineralogical  composition  ?  What  of  their  origin  ? 


38  FIRST     PRINCIPLES     OF     GEOLOGY. 

of  instances,  perhaps,  the  only  distinction  between  them 
and  the  volcanic  rocks  which  admit  of  recognition  is,  that 
the  former  are  more  ancient  than  the  latter. 

Some  of  them  were  evidently  ejected  after  the  manner  of  molten  lava ;  some 
must  have  been  scattered  abroad  as  showers  of  volcanic  dust  and  ashes ;  while 
others  (i.  e.,  the  highly  crystalline  and  compact  varieties)  have  undoubtedly 
consolidated  under  the  enormous  pressure  of  superincumbent  strata,  or  at  the 
bottom  of  an  ocean,  under  water. 

The  igneous  action  of  masses  of  trap  upon  the  aqueous  or  sedimentary 
rocks  is  also  marked  and  peculiar ;  the  latter,  at  the  points  of  contact,  being 
generally  indurated,  and  often  greatly  altered,  as  if  subjected  to  the  influence 
of  intense  heat ;  sandstones  in  some  instances  being  converted  into  quartzites, 
soft  limestones,  into  crystalline  marbles,  coal  into  coke,  and  clays  into  flinty, 
porcelain-like  masses. 

39.  The  varieties  of  trap  which  prevail  most  extensively 
and  which  preserve  sufficient  uniformity  of  composition 
and  aspect  to  allow  of  general  recognition,  are  as  follows  : 
BASALT,  GREENSTONE,  PORPHYRY,  AMYGDALOID,  and 
TRAP-TUFF. 

TJte  basalts  are  the  hardest,  most  compact, 
and  heaviest  of  the  trap-rocks.  .  They  are  usu- 
ally of  a  black  or  greenish-black  color,  of  a 
finegrained  texture,  and  very  frequently  ex- 
hibit a  more  or  less  columnar  or  prismatic  struc- 
ture— the  columns  or  prisms  having  three,  five, 
or  more  sides,  regular  and  jointed.  (See  Pig.  12.) 
Greenstone  is  a  general  designation  for  the 
hard,  granular-crystalline  varieties  of  trap.  The 
term  has  reference  to  their  usual  greenish  or  blackish-green  colors.  Their 
weathered  surfaces  acquire  a  dull,  dark-brown  color,  and  ars  often  covered 
with  patches  of  white  lichens.  As  compared  with  the  basalts,  the  green- 
stones are  less  compact,  more  granular,  exhibit  more  clearly  their  component 
crystals,  and  are  usually  massive  or  tabular  in  their  structure. 

Those  varieties  of  greenstones  and  traps  which  are  composed  essentially 
of  feldspar  and  augite  have  received  the  name  of  dolerites  (Gr.,  do/Upiref,  de- 
ceptive), from  the  difficulty  of  distinguishing  their  constituent  minerals ;  while 
those  composed  chiefly  of  feldspar  and  hornblende,  whose  composition  is  less 
mistakable,  have  been  called  diorites  (Gr.,  tiiupo^  a  clear  distinction). 

The  term  porphyry  (Gr.,  iropovpa,  purple)  was  originally  applied  to  a  red- 
dish rock  of  igneous  origin  found  in  Egypt,  and  much  used  for  ornamental 

QUESTIONS. — What  action  has  trap  often  exerted  on  other  rocks  which  are  in  contact 
•with  it?  What  are  the  principal  varieties  of  trap?  Describe  the  basalts.  What  are  the 
greenstones  ?  What  are  dolerites  and  diorites  ?  What  is  porphyry  ? 


TRAPPEAN     BOCKS. 


39 


FIG.  13. 


purposes.  It  is  now,  however,  employed 
by  geologists  to  designate  any  rock 
(whatever,  its  color)' which  contains  de- 
tached crystals  imbedded  in  a  compact 
base  or  matrix.  (See  Fig.  13.)  Rocks 
thus  constituted  are  very  characteristic 
of  the  trap  group,  but  do  not  belong  ex- 
clusively to  it. 

When  porphyry  is  spoken  of  in  gen- 
eral terms,  the  base  is  understood  to  bo 
It-ldspar,  with  imbedded  crystals  of  feld- 
spar but  when  the  base  is  some  other 
mineral  compound,  as  basalt,  greenstone, 
granite,  etc.,  the  porphyry  receives  a  dis-  < 

tinctive  name  from  the  basic  material ;  and  thus  we  have  basaltic  porphyry, 
greenstone  porphyry,  porphyritic  granite,  etc.,  etc. 

The  term  amygdaloid  (Gr.  cijuvydafaa,  an  almond),  is  applied  to  certain 
rocks,  especially  abundant  in  the  trap  series,  which  contain  small  rounded, 
vesicular  cavities  partially  or  entirely  filled  with  crystalline  deposits  of  dif- 
ferent minerals.  These  minerals,  being  of  a  different  color  from  the  mass  of 
the  rock  in  which  they  are  imbedded,  have  somewhat  the  appearance  of 
almonds  in  a  cake,  and  hence  the  terms  amygdaloid  and  amygdaloidal  The 
crystalline  deposits  found  in  amygdaloids  are  generally  carbonate  of  lime 
(calcspar),  agate,  jasper,  quartz,  etc.  Fig.  14  represents  a  specimen  of  vesi- 
cular lava,  in  ono  half  of  which  the  cavities  or  vesicles  are  empty,  while  the 
other  part  is  amygdaloidal,  i.  e.,  the  cavities  being  filled  with  carbonate  of 
lime,  which  appears  as  white  kernels. 

The  trap-tuffs  or  tufas  do  not  differ  essentially  from  those  of  volcanic  origin. 


FIG.  14. 


In  addition  to  the  general  divisions 
of  the  trap  rocks  above  described, 
different  geological  writers  further 
recognize  a  great  number  of  other 
varieties  or  sub-species.  The  follow- 
ing are  the  ones  which  the  student 
will  be  most  likely  to  meet  with  in 
his  reading  or  collections: — 

Clinkstones  or  phonolites  differ  little 
from  the  basalts  in  composition,  but 
are  less  compact,  and  break  up  into 
slate-like  fragments  ;  when  struck  by 
the  hammer,  they  emit  a  ringing  me- 
tallic sound — whence  the  name. 
Claysione  is  an  earthy,  compact  stone 


QUESTION. — What  is  an  amygdaloid  I    What  is  said  of  the  trap-tuffs  ?    What  are  some 
of  the  other  varieties  of  the  trap  rockc  " 


40         FIRST     PRINCIPLES     OF      GEOLOGY. 

of  a  purplish  color,  and  having  tho  aspect  and  texture  of  a  baked  or  in- 
durated clay.  Hornstone  (petro-silex  or  rock-flint]  is  a  compact,  highly  silicious 
rock,  with  very  much  the  aspect  of  a  tough,  massive  Hint ;  it  has  various 
colors  and  is  often  translucent.  Other  varieties  of  trap  or  porphyritie  rocks 
are  known  as  melaphyre,  aphanite,  euphotids,  diallage,  diabase,  etc. 

40.  Geographical  Distribution . — The  geographical  area  occu- 
pied by  the  trap  rocks  is  very  extensive.  In  South  America  trachytic  rocks, 
holding  an  intermediate  place  between  the  trappean  and  volcanic  rocks,  have 
an  enormous  development,  and  in  the  chain  of  the  Andes,  of  which  they 
form  tho  summit,  the  beds  are  sometimes  18,000  feet  in  thickness,  as  at 
Chimborazo  and  the  volcano  Pinchincha.  In  the  United  States  the  trap  rocjvs 
are  mostly  referred  to  tho  class  of  greenstones,  and  are  extensively  developed. 
In  the  Atlantic  States  three  belts  or  ranges  occur,  which  belong  to  the  east- 
'ern  slope  of  the  Appalachian  and  Green  Mountains,  and  are  co-extensive  with 
them.  One  belt,  the  eastern,  begins  in  Rhode  Island  and  extends  entirely 
across  the  eastern  part  of  Massachusetts  into  New  Hampshire,  and  also  en- 
circles in  part  Massachusetts  Bay.*  The  second  belt  runs  up  tho  valley  of 
the  Connecticut  river  and  passes  entirely  across  the  States  of  Connecticut 
and  Massachusetts,  terminating  at  New  Haven  in  the  well-known  "  East" 
and  "West  Rock."  Tho  most  prominent  elevations  of  this  range  are  Mt. 
Holyoke  and  Mt.  Tom  on  opposite  sides  of  the  Connecticut  river,  near 
Northampton  in  Massachusetts.  The  third  belt  of  trap  or  greenstone  occu- 
pies a  part  of  the  valley  of  the  Hudson  River,  appearing  conspicuously  and 
forming  the  bold  continuous  bluff,  in  the  southern  portion  of  the  valley,  termed 
the  "  Palisades."f  This  belt  is  prolonged  through  New  Jersey,  and  may  bo 
traced,  with  a  few  interruptions,  through  Pennsylvania,  Virginia,  North  and 
South  Carolina,  and  into  Georgia.:}:  Trappean  rocks  are  very  abundant  upon 
Lake  Superior  and  mainly  constitute  the  well-known  promontory  "  Kewau- 
nee  Point"  and  also  "Isle  Royal."  Upon  the  western  slope  of  tho  Rocky 
Mountains,  near  the  head  waters  of  tho  Columbia  and  Colorado  Rivers,  trap 


QUESTIONS. — What  is  said  of  the  geographical  distribution  of  the  trap  rocks?  What  are 
their  prominent  features  in  the  United  States  ? 


*  This  belt,  or  rather  area  of  greenstone,  is  prominently  exhibited  in  Wcston,  "Wal- 
tham,  Lexington,  Woburn  and  Wrentham  in  Massachusetts,  and  onward  to  Ipswich  in 
New  Hampshire.  It  also  presents  very  striking  and  easily  recognized  features  at  Na- 
hant,  Salem,  Marblehead,  and  at  numerous  points  upon  the  coast  of  Mjiine  and  Nova 
Scotia. 

t  "  This  locality  may  be  regarded  as  a  typical  representation  of  trap." — EMMONS. 

$  This  range  of  trap  extends  through  New  Jersey  in  nearly  continuous  ridges,  and 
forms  several  conspicuous  elevations  between  New  York  City  and  Newark.  In  Penn- 
sylvania it  is  conspicuous  in  the  north-eastern  counties,  i.  e.,  Burke,  Montgomery  and 
Chester.  The  "  Coneaeaga  Hills"  of  Pennsylvania  are  trap.  In  Virginia  the  trap  range 
appears  between  Fredericksburg  and  Buckingham  County,  and  pursues  a  southwest  di- 
rection into  Rockingham  County,  N.  C.,  continuing  to  the  Yadkin.  Another  branch  be- 
gins near  Oxford,  Granville  County,  N.  C.,  and  extends  into  South  Carolina,  terminat- 
ing apparently  in  the  Chesterfield  District. 


GRANITIC     ROCKS.  41 

rocks  arc  probably  developed  to  a  greater  extent  than  in  any  other  portion 
of  the  North  American  Continent. 

41.  Surface  Configuration  of  Trap  Districts. — Districts 
abounding  in  trappean  rocks  exhibit  a  greater  diversity  of  surface  than  is  oc- 
casioned by  the  presence  of  almost  any  other  geological  formation — the  char- 
acteristic features  being  long,  low  ranges  of  hills  with  a  peculiar  undulating 
outline,  detached  and  isolated  conical  eminences,  step-like  ascents,  abrupt 
crags,  and  often  perpendicular  walls  of  great  height  and  length  (e.  </.,  the 
Palisades  of  the  Hudson) — the  whole  producing  scenery  extremely  picturesque 
and  beautiful.  The  soil,  also,  resulting  from  the  decomposition  of  trap,  as 
w%ll  as  from  most  volcanic  rocks,  K  generally  remarkable  for  fertility,  while 
the  natural  joints  and  fissures  peculiar  to  rocks  of  this  formation  establish  an 
effective  drainage. 

<12.  Industrial  Applications . — Many  of  the  varieties  of  trap  af- 
ford very  durable  building  materials,  but  the  difficulty  of  dressing  them  into 
proper  shape,  combined  with  their  dingy  and  unattractive  colors,  restricts  their 
application  to  architectural  purposes.  Their  hardness,  however,  renders  them 
peculiarly  fitted  for  the  construction  of  roads  and  for  "macadamizing."  Ba- 
salt, artificially  melted  and  cooled  rapidly,  is  converted  into  a  kind  of  obsid- 
ian (volcanic  glass)  undistinguishable  by  any  external  characters  from  that 
derived  from  volcanic  districts.  Such  an  artificial  obsidian  is  now  manufac- 
tured in  Birmingham,  England,  and  cast  into  ornamental  blocks  and  moldings. 

Rocks  of  trappean  origin  rarely  afford  available  supplies  of  the  metals. 
The  wonderfully  rich  deposits  of  native  copper  in  the  vicinity  of  Lake  Su- 
perior occur,  however,  in  trap  rocks,  and  are  a  notable  exception  to  the  rule. 
The  amygdaloids  and  trap- tuffs  abound  in  "  geodes"  or  rounded  nodules  having 
internal  cavities  lined  with  crystals  of  quartz  or  amethyst,  or  concentric 
layers  of  agate,  carnelian,  chalcedony,  or  other  minerals ;  and  it  is  from  this 
source  that  most  of  the  above-named  gems,  made  use  of  by  lapidaries  and 
jewelers,  are  obtained.  In  external  appearance  a  geode  is  generally  an  ir- 
regular spherical  mass  of  mineral  matter,  but  exhibits  a  beautiful  internal 
structure  when  fractured. 

SECTION     III. 
GRANITIC     ROCKS. 

43.  This  series  of  rocks  derives  its  name  from  granite, 
its  principal  member.  They  are  all  highly  crystalline,  and 
none  of  their  crystals  are  rounded  or  water- worn. 


QUESTIONS. — What  is  the  surface  configuration  of  the,  trap  districts  ?  What  are  the 
industrial  applications  of  the  trap  rocks  and  their  associated  minerals?  What  are 
"  geodes  ?"  What  is  the  general  character  and  position  of  the  granitic  rocks  ? 


42 


FIRST     PRINCIPLES      OF     GEOLOGY. 


They  occur,  for  the  most  part,  in  the  crust  of  the  earth, 
as  mountain  masses  or  veins,  bursting  through  and  pushing 
up  the  sedimentary  rocks  into  inclined  and  unnatural  po- 
sitions. (See  Fig.  15.) 

FIG.  15. 


44.  Typical  or  True  Granite  is  composed  of  three  min- 
erals— feldspar,  quartz  and  mica — promiscuously  inter- 
mixed, in  the  form  of  distinct  grains  or  crystals. 

The  proportions  of  these  three  constituents  vary  indefinitely,  with  this  lim- 
itation, that  the  feldspar  is  always  an  essential  ingredient,  and  never  forms 
less  than  a  third,  rarely  less  than  a  half  of  the  mass,  and  generally  a  still 
larger  proportion.  Sometimes  the  mica,  sometimes  the  quartz,  becomes  so 
minute  as  to  be  barely  perceptible.  The  state  of  aggregation  of  tho  mass, 
also,  varies  greatly  ;  some  granites  being  very  close  and  fine-grained,  whiles 
others  are  largely  and  coarsely  crystalline. 

Masses  of  granite  ocaur  in  Norway  with  feldspar  crystals  of  a  cubic  foot, 
mica  crystals  of  a  square  foot  in  dimensions,  and  the  quartz  in  still  more  con- 
siderable masses — at  ouo  place  twenty-one  feet  thick — extending  between 
them.  In  other  cases,  granite  of  a  uniform  and  extremely  fine  ;rain  may  bo 
seen  upon  the  sides  of  some  mountains,  covering  acres  of  surface,  without  a 
crack  or  a  seam. 

The  colors  of  granite  are  generally  red,  gray  or  white. 

45.  Varieties  of  Granite . — In  addition  to  feldspar,  quartz  and 
mica,  or  in  place  of  one  or  two  of  these  ingredients,  other  minerals  frequently 
occur  in  granite,  giving  rise  to  numerous  varieties  or  sub-species.  Of  those 
the  following  are  the  most  important : — 

"When  hornblende  replaces  the  mica  found  in  true  granite,  the  rock,  although 
not  essentially  changed  in  character,  is  termed  Syenite,  from  Syene,  in  Upper 
Jigypt,  where  it  was  early  known  and  quarried.  When  hornblende  and  mica 
are  both  found  in  the  same  variety  of  granite,  the  rock  is  termed  Syenitic 

QUESTIOMS  —  What  is  the  composition  of  true  granite  ?  What  are  the  prevailing  colors 
of  granite  ?  What  constitutes  varieties  in  granite  ?  What  is  Syenite  ? 


GRANITIC     ROCKS. 


43 


granite.  Much  of  the  so-called  Massachusetts  (Quincy)  granite,  famous  for  its 
architectural  applications,  is  syenite, — the  hornblende  being  frequently  in  very 
small  proportion.  Examples  of  this  rock  in  construction  may  be  seen  in 
Bunker  II ill  Monument,  the  custom-house  and  court-house  in  Boston,  the 
Merchants'  Exchange  and  Astor  House  in  New  York  City,  and  the  custom- 
house in  New  Orleans. 

When  talc  occurs  in  the  place  of  mica,  the  admixture  of  feldspar,  quartz 
and  talc  is  called  Protogene,  or  talcose  granite. 

Graphic  granite  is  composed  of  flesh-colored  or  white  feldspar,  intermixed 
with  thin  and  irregularly-shaped  laminae  (plates)  of  quartz.  A  section  across 
the  cads  of  these  laminas  exhibits  the  appearance  of  Arabic  or  hieroglyphic 
writing  upon  the  feldspar  tablet ;  hence  the  name.  Fig.  16  is  a  fac-simile  of 
a  section  of  graphic  granite  from  Goshen,  Mass. 

FIG.  16. 


Hypersthene  rock,  or  hypersthenic  granite,  is  the  name  given  to  a  rock 
having  the  massive  structure  of  granite,  which  is  composed  mainly  of  labra- 
dorite  (a  variety  of  feldspar)  and  hypersthene  (a  mineral  allied  to  hornblende). 
It  is  of  a  gray  or  bluish-gray  color,  and  is  found  most  abundantly  in  the  United 
States  in  the  district  of  the  Adirondack  Mountains,  in  New  York. 

When  a  granite,  in  addition  to  the  aggregated  crystals  composing  the  gen- 
eral mass  of  the  rock,  contains  largo  and  distinct  crystals  of  feldspar,  it  is 

FIG.  17. 


QUESTIONS.— What  are  examples  of  syenite  in  construction?     What  is  protogene? 
What  graphic  granite  ?    What  hypersthene  rock  ?    When  is  granite  termed  porphyritic  ? 


44          FIRST     PRINCIPLES     OF     GEOLOGY. 

termed  porpliyriiic.  Fig.  17  represents  a  marked  example  of  porphyritic 
granite  from  Cornwall,  England,  figured  by  Sir  Charles  Lyell.  Fine  speci- 
mens of  porphyritic  granite  may  be  obtained  in  the  vicinity  of  Lake  Mem- 
phremagog,  Vermont. 

Beside  the  preceding,  there  are  many  other  granitic  compounds,  in  all  of 
which  feldspar,  quartz,  mica  and  hornblende  are  the  principal  ingredients, 
and  talc,  hypersthene,  chlorite  and  schorl  the  chief  modifying  or  accidental 
minerals.  Sometimes  half  a  dozen  varieties  of  granite  may  be  found  in  the 
same  district,  or  even  in  a  single  quarry. 

Origin  of  Granite . — The  granites  differ  little  in  chemical  composition 
from  the  trappean  and  volcanic  rocks — silica,  alumina,  lime,  magnesia,  pot- 
assa,  soda  and  oxyd  of  iron  being  common  ingredients  of  all.  These  sub- 
stances, combined  in  different  proportions  and  under  different  circumstances 
of  pressure,  etc.,  may  yield  a  porous  lava,  a  compact  trap,  or  a  crystalline 
granite. 

All  the  varieties  of  granite  preserve  certain  characteristic  features  in  com- 
mon. They  are,  for  example,  more  crystalline  than  any  other  igneous  rocks  ; 
they  are  never  porous  and  vesicular  like  recent  lavas ;  and  never  amygda- 
loidal,  like  many  of  the  traps.  They  are,  moreover,  rarely  found  overlying 
other  rocks,  as  trap  is  often  seen  to  do. 

On  the  other  hand,  instances  are  cited  where  contiguous  masses  of  granite 
and  trap  imperceptibly  blend  into  each  other ;  and  it  is  alsb  claimed,  that 
granite,  like  trap  and  lava,  indurates  and  alters  (as  if  with  intense  heat)  rocks 
of  other  formations  with  which  it  comes  in  contact.  Granite,  like  trap  and 
lava,  is  also  an  "  eruptive"  rock.  Geologists,  therefore,  have  been  led  very 
generally  to  the  opinion  that  the  granitic  rocks  were  originally  melted  at 
great  depths  in  the  earth  and  subsequently  cooled  and  consolidated  under  im- 
mense pressure  and  with  extreme  slowness ;  and  that  to  these  conditions  they 
owe  their  crystalline  structure,  as  well  as  that  compactness  which  is  wanting 
to  most  lavas  and  to  the  slag  produced  by  melting  granite  artificially.  The 
compactness  of  the  trap  rocks  over  the  volcanic  is  also  ascribed,  in  a  degree, 
to  similar  conditions  of  formation. 

This  generally-received  theory  of  the-  igneous  origin  of  granite  has,  how- 
ever, within  a  recent  period,  been  questioned  or  disputed  by  not  a  few  able 
chemists  and  geologists.  Admitting  that  the  mineral  constituents  of  granite 
have  been  in  a  fluid  or  partially  fluid  state,  they  ascribe  this  result  to  the 
solvent  action  of  chemical  solutions,  aided,  it  may  be,  by  moderate  degrees 
of  temperature,  rather  than  to  fusion  by  intense  heat.  Some  of  the  arguments 
which  have  been  brought  forward  in  support  of  this  view  are  as  follows :  — 

In  granite  quartz  is  the  most  recent  mineral     This  seems  evident  from  the 


QUESTIONS. — "What  is  said  of  the  chemical  composition  of  granite  ?  In  what  do  the 
granites  especially  differ  from  the  traps  and  lavas?  What  is  the  generally  received 
theory  respecting  the  origin  of  granite?  What  other  view  is  entertained?  What  are 
some  of  the  facts  opposed  to  the  igneous  theory  ? 


GRANITIC     ROCKS.  45 

circumstance  that  the  quartz  is  found  to  occupy  the  space  left  by  the  other 
constituents  of  the  rock,  i.  e.,  mica,  feldspar,  etc.,  and  also  presents  impres- 
sions of  the  crystals  of  the  associated  minerals  without  their  edges  or  angles 
appearing  in  any  way  broken  or  rounded.*  But  quartz  is  much  less  fusible 
than  either  mica  cr  feldspar,  and  consequently  would  have  crystallized  and 
consolidated  first,  had  the  whole  mass  of  the  rock  been  melted.  That  it  has 
not  so  happened,  is  claimed  to  be  entirely  inconsistent  with  any  hypothesis 
of  igneous  fusion. 

Granite  veins,  not  thicker  than  fine  wire  or  ordinary  writing-paper,  in  some 
instances  traverse  rocks  of  other  formations  for  a  considerable  distance.  The 
advocates  of  the  igneous  origin  of  granite  suppose  that  these  veins  have  been 
formed  by  the  injection  of  molten  mineral  matter  into  fissures  previously  ex- 
isting ;  the  opponents  o^  this  theory,  on  the  contrary,  maintain  that  gradual 
solidification  and  cooling — conditions  deemed  essential  to  a  crystalline  struc- 
ture— would,  under  such  circumstances,  be  impossible.  The  occasional  pres- 
ence in  granite  of  minerals  containing  a  considerable  proportion  of  water  in 
combination,  is  also  regarded  as  inconsistent  with  the  supposition  that  the 
constituents  of  the  rock  have  been  subjected  to  the  continued  action  of  in- 
tense heat. 

These  and  other  similar  arguments  have,  therefore,  induced  many  geologists 
to  entirely  abandon  the  theory  which  ascribes  to  granite  an  exclusively  ig- 
neous origin  ;  while  others — perhaps  a  majority — still  regard  the  evidence  in 
favor  of  the  igneous  theory  as  sufficiently  satisfactory.! 

Industrial  Applications,— Granite  holds  the  first  rank 
among  building  stones  for  durability.  The  finer  varieties 
are  susceptible  of  a  good  polish,  and  retain  it  for  a  long 
time  under  all  atmospheric  influences  ;  granite,  moreover, 
does  not  readily  become  stained  by  vegetation,  and  when 
carved  preserves  its  sharp  edges  longer  than  any  other  rock 
used  for  architectural  purposes.:]:  To  crush  a  half  inch 
cube  of  the  best  granite  requires  a  pressure  of  24,500  Ibs. 


*  This  "order  of  succession"  in  the  constituents  of  granite  may  be  seen  to  advantage 
in  the  coarsely  crystalline  specimens. 

t  The  author,  although  favoring  the  most  recent  views,  has  nof  thought  it  expedient, 
i:i  an  elementary  text-book,  to  depart  from  the  usual  classification  which  assigns  to  gran- 
ite a  place  among  the  igneous  rocks.  Whatever  theory  may  finally  prevail,  the  student 
in  possession  of  the  facts  as  above  given  can  not  well  be  led  into  error.  Those  desirous 
cf  further  information  will  find  a  full  exposition  of  the  modern  views  respecting  the 
origin  of  the  crystalline  rocks  in  Bischof's  "  Chemical  Geology,"  English  translation. 

%  The  pedestal  of  the  statue  of  Peter  the  Great,  at  St.  Petersburg,  consists  of  a  single 
perfect,  block  of  granite  from  Finland,  weighing  1280  tons :  while  a  monolithic  statue 
of  red  granite,  OK  the  eite  of  ancient  Memphis,  sixty  feet  in  height,  has  an  estimated 
weight  of  887  tons. 


FT  rn  t 


46  FIRST     PRINCIPLES     OF     GEOLOGY. 

Granite  is  commonly  sold;  in  the  rough  block,  by  the  ton 
of  fourteen  cubic  feet,  or,  if  dressed,  by  the  superficial  foot 
of  hammered  surface. 

Granitic  rocks  often  contain  veins  of  metalliferous  ores, 
which  are  commonly  found  most  productive  near  the  line 
of  contact  between  the  granite  and  other  formations.  They 
are  also  the  repositories  of  many  interesting  minerals  and 
gems.  The  finest  porcelain  clays  (kaolin)  result  from  the 
decomposition  of  the  highly  feldspathic  varieties  of  granite. 

46.  Distribution  of  Granite,— Granite  is  one  of  the  most 
easily  recognized  and  widely  distributed  of  all  rocks.  It 
forms  the  principal  mass  or  axis  of  most  of  the  great 
mountain  ranges  of  the  globe,  although  it  rarely  reaches 
the  most  elevated  summits  ; — Mt.  Blanc  in  Switzerland 
being  the  highest  known  peak  of  granite. 

In  all  the  New  England  States  granite  is  most  abundant ;  the  most  cele- 
brated quarries  being  at  Quincy,  Mass,  (where  the  rock  is  a  syenite),  and 
upon  the  coast  of  Maine.  Some  of  the  quarries  in  the  latter  State  are  ca- 
pable of  furnishing  perfect  blocks  of  fine  grained  granite  from  thirty  to  sixty 
feet  in  length.  Granites  and  syenites  abound  in  the  southern  Highlands  of 
the  Hudson  and  along  the  shores  of  Delaware  Bay.  A  granite  obtained  on 
Staten  Island,  and  much  used  for  paving  in  New  York  City,  is  remarkable  for 
its  density,  a  cubic  foot  of  it  weighing  over  180  Ibs. ;  while  that  of  Quincy 
weighs  only  165  Ibs.  In  Virginia  granite  is  not,  comparatively  speaking, 
abundant;  the  principal  variety — occurring  on  the  low  ranges  of  the  Blue 
Ridge — being  composed  mainly  of  quartz  and  feldspar.  A  ridge  of  granite 
forms  the  first  waterfalls  of  the  Rappahanock,  James,  Roanoke,  Neuse,  Tar 
and  Capo  Fear  Rivers.  In  South  Carolina  and  Upper  Georgia  the  formation 
is  finely  developed,  and  at  Abbeville,  S.  C.,  the  rock  can  scarcely  be  distin- 
guished from  that  at  Quincy.  The  famous  stone  mountain  of  De  Kalb  Co., 
Ga.,  is  a  huge  mass  of  granite  rising  almost  perpendicularly  several  hundred 
feet  above  the  surrounding  country. 

In  the  highlands  of  "Wisconsin  and  Michigan,  on  the  northern  side  of  Lake 
Superior  and  Lake  Huron,  and  between  the  Upper  Mississippi  and  Lakes  Su- 
perior and  Michigan,  granites  and  syenites  abound. 

Upon  the  Pacific  coast  granite  is  a  constituent  part  of  all  the  great  mount- 
ain ranges  of  Oregon  and  California. 

QUESTIONS. — What  is  said  of  the  distribution  of  granite?  What  are  somn  of  its  most 
famous  quarries  in  the  United  States?  What  of  its  occurrence  in  the  Southern  States 
and  at  the  West  ? 


AQUEOUSEOCKS.  47 

47.  Surface    Configuration    of   Granitic    Districts. — The 

physical  aspect  of  purely  granitic  districts  is  in  general  sombre  and  monoton- 
ous— hills  with  a  heavy  rounded  outline  and  slightly  undulating  plains  being 
the  characteristic  features.  Partly  from  their  elevated  and  exposed  situation 
as  mountain  chains  and  table  lands,  and  partly  from  the  barren  nature  of  theii 
scanty  soil,  granitic  areas  also  offer  but  few  inducements  for  the  agriculturist 
Some  of  the  most  barren  and  unfertile  portions  of  New  England  are  her 
granitic  districts. 


CHAPTER    V. 

VARIETIES  AND  LITHOLOG-ICAL  CHARACTERS  OF  THE 
AQUEOUS  ROCKS. 

48.  IT  is  admitted  by  all  geologists  that  the  aqueous 
rocks  have  resulted,  either  directly  or  indirectly,  from  a 
disintegration  and  breaking  down  of  the  igneous  rocks  and 
a  rearrangement  of  their  particles  ;  and  that  the  agencies 
by  which  these  results  have  been  effected  have  been  me- 
chanical, chemical  and  organic. 

The  special  action  of  each  of  these  various  forces  will  be  considered  here- 
after in  detail,  but  at  present  our  attention  is  to  be  directed  to  results  rather 
than  causes.  "  "We  are  compelled,"  says  Mr.  Jukes,  "  to  look  upon  the  purely 
igneous  rocks  as  original  productions.  We  can  only  speculate,  and  that  very 
vaguely,  on  what  was  the  conditions  of  the  materials  which  compose  them 
previously  to  their  being  placed  an  a  molten  or  plastic  state,  in  the  positions 
where  they  subsequently  consolidated.  But  in  our  examination  of  the  aqueous 
rocks  we  can  go  a  stop  further  back,  and  learn,  either  accurately  or  approxi- 
mately, whence  the  materials  composing  them  were  derived,  and  what  was 
their  previous  condition." 

49.  Aqueous  Rocks  Mechanically  Formed, — Theagencies 
concerned  in  the  production  of  these  rocks  are,   moving 
water  (including  ice)  and  moving  air. 

All  the  earthy  matters  we  see  around  us,  the  mud,  the  clay,  the  soil,  tho 
sand,  tho  dust,  the  gravel  and  tho  rounded  rocks  and  pebbles,  are  only  so 

QUESTIONS. — What  is  the  general  surface  configuration  of  granitic  districts?  In  what 
manner  have  the  aqueous  rocks  been  formed?  What  mechanical  agencies  have  been 
concerned  in  the  formation  of  the  aqueous  rocks  ? 


48          FIRST      PRINCIPLES     OF     GEOLOGY. 

much  raw  material  in  the  process  of  manipulation.  They  may  bo  likened  to 
the  refuse  and  the  chips  of  some  vast  manufactory.  They  are  the  building 
materials  of  the  stratified,  sedimentary  rocks,  which  are  being  carried  from 
the  quarry  to  the  place  of  construction.  Every  pebble,  every  grain  of  sand, 
every  atom  of  mud  is  a  fragment  of  a  pre-existing  rock,  removed  at  some  pe- 
riod of  past  time  and  destined  ultimately  to  enter  into  the  structure  of  some 
other  rock  in  the  future. — JUKES. 

50.  Alluvium, — This  term  (from  the  Latin  ad,  together," 
and  lucre,  to  wash)  is  usually  understood  to  refer  to  mat- 
ter washed  or  brought  together  by  the  ordinary  operations 
of  water. 

The  soil  and  sands  of  river  banks,  deposited  from  overflows,  of  plains  which 
have  been  once  the  sites  of  lakes,  or  estuaries  of  the  sea,  and  the  sand  and 
mud  resulting  from  tidal  action,  are  considered  as  alluvial. 

Drift  or  Diluvium  (Lat.  dis,  asunder,  and  lucre,  to  wash) 
is  the  name  given  to  accumulations  of  abraded  materials — 
sand,  clay,  gravel  and  fragments  of  rocks — brought  together 
or  produced  by  the  apparently  violent  action  of  water,  or 
water  and  ice  conjointly. 

51.  Soil  is  merely  disintegrated  and  decomposed  rock, 
containing  a  variable  proportion  of  organic  matter,  the 
product  of  decomposed  vegetable  or  animal  substances. 

The  principal  mineral  constituents  of  soils  are  silica  (sand),  alumina,  lime, 
magnesia  and  oxyd  of  iron ;  of  these  silica  is  the  most  abundant,  and  fre- 
quently forms  nine  tenths  of  the  entire  weight  of  the  soil.  Good  arablo  soil, 
in  addition,  always  contains  small  quantities  of  potash,  soda  and  phosphoric 
acid. 

The  relative  proportions  of  sand,  clay  and  lime  in  soils  give  to  them  cer- 
tain peculiar  physical  characters.  A  soil  in  which  sand  predominates  is  light 
and  porous ;  an  excess  of  clay,  on  the  other  hand,  renders  it  heavy  and  re- 
tentive of  moisture.  The  best  soils  are  those  in  which  the  earthy  constitu- 
ents are  so  proportioned  that  the  light,  porous  qualities  of  one  are  balanced 
by  the  close,  retentive  properties  of  the  other. 

The  quantity  of  organic  matter  (humus)  derived  from  the  decomposition  of 
animal  or  vegetable  substances  present  in  a  soil  essentially  modifies  its  char- 
acter. The  average  amount  of  organic  matter  contained  in  soils  is  about  five 


QUESTIONS— What  is  alluvium  ?  What  is  drift  or  diluvium  ?  What  is  a  soil  ?  What 
are  the  principal  mineral  constituents  of  soils?  What  gives  to  a  soil  its  physical  charac- 
teristics ?  What  is  said  of  the  organic  constituents  of  soils  ? 


AQUEOUSROCKS.  49 

per  cent.  Fertile  alluvial  soils,  or  those  deposited  from  water,  are  generally 
characterized  by  the  presence  of  a  much  larger  proportion,  and  in  some  peaty 
soils  the  amount  may  exceed  seventy  or  eighty  per  cent. 

The  presence  of  organic  matter  in  a  soil  is  easily  proved  by  igniting  a  thor- 
oughly dried  portion  and  noting  the  loss  of  weight  consequent  upon  the  ope- 
ration. 

52.  Gravel  is  the  term  applied  to  the  water- worn  frag- 
ments of  rocks,  when  the  pebbles  or  particles  vary  from  the 
size  of  a  pea  to  that  of  a  hen's  egg.     It  is  generally  com- 
posed of  fragments  of  the  harder  and  more  silicious  rocks 
— as  these  longest  resist  the  process  of  attrition. 

53.  Bowlders  are  detached  masses  of  rock,  generally  of 
a  rounded   form,  scattered  over  the   soil  or  distributed 
throughout  the  surface  material.     They  are  often  of  im- 
mense size  and  are  not  necessarily  like  the  rocks  which  are 
contiguous  or  underlying. 

Fig.  18  represents  the  appearance  and  distribution  of  bowlders  at  a  locality 
on  Cape  Ann,  Massachusetts. 

FIG.  18. 


54.  Conglomerates  are  cemented  masses  of  gravel  and 
pebbles  of  all  sizes  ;  in  other  words,  consolidated  gravel. 


QTTE6TION6.— Ho-w  may  the  presence  of  organic  matter  in  soils  be  determined  ?    What 
is  gravel  ?    What  are  bowlders  ?    What  are  conglomerates  ? 

3 


50          FIRST     PRINCIPLES     OF     GEOLOGY. 

They  are  sometimes  termed  "  pudding-stones/'  from  the 
fancied  resemblance  of  their  pebbles  to  the  fruit  in  a  plum- 
pudding. 

"When  the  term  "  conglomerate"  is  used  alone,  we  usually  understand  a 
mass  of  quartz  pebbles  united  by  a  silicious  sand  or  cement ;  but  when  the 
pebbles  consist  of  trap,  limestone,  slate  or  other  rock,  the  fact  is  denoted  by 
calling  them  trappean,  calcareous  or  slaty  conglomerates,  etc.* 

55.  Breccias  are  compacted  masses  of  irregular,  angular 
fragments  ;  whereas  in  conglomerates  the  component  peb- 
bles are  always  rounded  and  water- worn. 

56.  Sandstone  is  simply  consolidated  sand,  the  particles 
being  compacted  by  pressure,  or  held  together  by  some  ce- 
menting material. 

Sandstones  exhibit  every  variety  of  color.  The  red  appearance  of  the 
sandstones  of  tho  valley  of  the  Connecticut,  of  New  Jersey,  North  Carolina, 
etc.,  is  mainly  due  to  the  covering  of  each  little  grain  with  peroxyd  of  iron, 
which  sometimes  acts  as  a  cement  to  the  stone  and  binds  its  particles  to- 
gether. Flakes  and  spangles  of  mica  occur  so  abundantly  in  some  sandstones, 
and  in  such  regular  seams,  as  to  cause  the  rock  surfaces  to  glitter  and  the 
rock  itself  to  split  into  thin  plates  or  slabs.  Such  sandstones  are  called  mica- 
ceous. 

A  sandstone  which  admits  of  being  freely  cut  and  worked 
by  the  builder  is  often  termed,  freestone. 

The  composition  of  clay  has  been  already  noticed.     (See  §  14,  page  19.) 

57.  Marl  is  a  loose  appellation  for  all  friable  compounds 
of  clay  and  lime  ;  when  the  clay  predominates  it  is  called 
an  aluminous  marl ;  but  if  the  lime  is  in  excess,  it  is 

QUESTIONS. — What  are  breccias  ?  What  is  a  sandstone  ?  What  is  the  occasion  of  the 
red  color  of  many  sandstones  ?  When  is  a  sandstone  said  to  be  micaceous  ?  What  is 
freestone  ?  What  is  marl  ? 


*  The  abundance  of  silica  in  sand,  gravel,  conglomerates,  etc.,  is  due  to  the  predomi- 
nance of  silicious  rocks  in  the  crust  of  the  earth,  as  well  as  to  their  great  durability  and 
mode  of  fracture.  Highly  silicious  minerals  are  not  easily  acted  upon  by  water  or  any 
other  common  solvent,  and  are  not,  therefore,  so  easily  disintegrated  by  chemical  force 
as  those  which  contain  lime  or  other  minerals.  On  the  other  hand,  quartzose  rocks, 
though  very  hard,  are  often  rather  brittle  and  tend  to  break  into  cubical  masses  rather 
than  into  plates  or  slabs.  These  'masses  are  soon  converted,  by  motion  in  water  and  the 
consequent  rounding  of  their  angles,  into  more  or  less  globular  pebbles,  and  are  moved  by 
tbe  action  of  currents  with  comparative  facility. — Jukes. 


AQITEOUSROCKS.  51 

termed  a  calcareous  marl.  "Shell-marl"  is  the  term  ap- 
plied to  such  varieties  as  contain  abundant  remains  of 
shells. 

58.  Loam  is  a  soft  and  friable  mixture,  containing  much 
clay,  sufficient  sand  to  render  the  mass  permeable  by  water 
and  prevent  plasticity,  some  iron,  and  a  varying  proportion 
of  organic  matter. 

59.  Shale  (Ger.  sckalen,  to  peel  or  scale  off)  is  a  term 
applied  to  such  argillaceous  (clayey)  rocks  as  split  with 
facility  into  irregular  plates  or  layers,  in  a  direction  paral- 
lel to  each  other  and  the  original  planes  of  deposition. 

60.  Slate, — This  term  is  often  applied  to  all  hard  rocks 
that  can  be  readily  split  up.     It  should,  however,  be  re- 
stricted to  the  highly  compact  and  indurated  argillaceous 
rocks,  like  roofing  slate,  which  split  with  great  regularity 
into  thin,  smooth  plates,  or  layers. 

In  true  slates  the  splitting  or  "  cleavage"  does  not  necessarily  take  place 
(as  in  shale)  in  lines  parallel  to  the  original  planes  of  deposition,  but  it  may 
be  at  right  angles  to  them. 

61.  Schist  is  a  term  often  used  as  synonymous  with  slate, 
but  is  properly  limited  to  argillaceous  rocks  more  highly 
indurated  than  slates  or  shales,  often  highly  crystalline  in 
texture,  and  which  split  either  with  the  bedding  or  across 
it,  but  with  much  less  facility  and  regularity  than  the 
elates. 

In  general,  a  rock  described  as  "  schistose"  is  understood  to  have  an  imper- 
fect slaty  structure,  but  the  transitions  from  shale  to  slato,  and  from  slate  to 
schist  are  often  so  gradual  as  to  be  hardly  discernible. 

62.  Aqueous   Rocks   of   Chemical  or  Organic  Origin,— 

Under  this  group  are  included  most  of  the  limestones 
(carbonate  of  lime),  with  the  exception  of  some  of  the 
more  highly  crystalline  varieties  (statuary  marble),  which 


QUESTIONS.— What  is  loam  ?  What  is  shale?  What  is  slate?  What  is  schist  ?  When 
is  a  rock  said  to  be  schistose?  What  aqueous  rocks  may  be  especially  referred  to  a 
chemical  or  organic  origin? 


52          FIRST     PRINCIPLES     OF     GEOLOGY. 

are  considered  as  metamorphic  ;  the  magnesian  limestones  ; 
silicious  sinter ;  infusorial  earths  ;  gypsum  (sulphate  of 
lime)  ;  rock-salt ;  coal  in  all  its  varieties,  etc.;  etc. 

Carbonate  of  lime  is  nearly  insoluble  in  pure  water  (dissolving  only  to  the 
extent  of  two  grains  to  the  gallon) ;  but  in  waters  charged  with  carbonic  acid 
gas  it  dissolves  freely.  The  waters  of  ordinary  springs,  rivers  and  lakes  al- 
ways contain  some  carbonic  acid,*  and  in  almost  all  of  them  carbonate  of 
lime  is  retained  in  solution  in  variable  proportions.  In  some  springs  it  occa- 
sionally reaches  the  point  of  saturation,  which  is  about  105  parts  in  100,000. 
In  the  river  Thames  the  quantity  of  carbonate  of  lime  present  has  been  esti- 
mated to  be  fifteen  parts  in  100,000  of  water;  in  the  Rhine,  at  Bonn,  9.4G 
parts  in  100,000,f 

Notwithstanding  the  immense  amount  of  carbonate  of  lime  continually 
carried  into  the  ocean  by  land- drainage,  the  quantity  found  in  sea-water  is 
very  small,  and  in  most  analyses  of  sea-water  it  is  not  mentioned  at  all.:}: 
This  curious  fact  has  been  accounted  for  on  the  supposition  that  carbonate  of 
lime  is  continually  abstracted  from  sea- water  by  marine  animals,  for  the 
formation  of  their  shells  and  other  hard  parts  of  their  structure. 

When  waters  containing  carbonate  of  lime  in  solution  are  agitated  or 
heated,  or  even  exposed  continuously  to  the  air,  the  carbonic  acid,  entirely  or 
in  part,  escapes,  and  the  lime  is  precipitated,  forming  incrustation?,  which  may 
be  often  noticed  in  the  channels  of  streams,  or  more  commonly  in  water-pipes 
and  on  the  sides  of  kettles  and  steam-boilers  (the  fur). 

63.  Stalactites  and  Stalagmites, — This  action  is  beau- 
tifully illustrated  in  the  formation  of  concretionary  calca- 
reous deposits  in  caverns,  termed  "  stalactites"  and  "  sta- 
lagmites." 

"Water  charged  with  carbonate  of  lime  and  carbonic  acid  falls  in  drops  from 
the  roof  and  sides  of  the  cavern ;  but  each  drop,  before  falling,  remains  sus- 
pended for  a  time,  during  which  it  loses,  by  evaporation,  both  water  and  car- 
bonic acid  gas,  and  its  solvent  power  being  thus  diminished,  a  minute  por- 


QIJESTIONS.— What  is  said  of  the  presence  of  carbonate  of  lime  in  water  ?  What  is  said 
of  the  presence  of  carbonate  of  lime  in  sea-water  1  When  will  carbonate  of  lime  be  pre- 
cipitated from  solutions?  Describe  the  formation  of  stalactites  and  stalagmites. 


*  Soils  rich  in  organic  matter  contain  much  carbonic  acid,  and  water,  in  percolating 
through  them,  is  capable  of  absorbing  it  to  the  extent  of  about  two  thirds  |of  its  bulk. 
Rain-water  and  snow,  also,  acquire  some  carbonic  acid  from  the  atmosphere. 

t  Bischof  calculated  that  the  mean  quantity  of  carbonate  of  lime  carried  into  the  sea 
by  the  Rhine  is  sufficient  for  the  yearly  formation  of  three  hundred  and  thirty-two  thou- 
sand millions  of  oyster  shells  of  the  usual  size. 

$  Other  combinations  of  liuic,  i.  c.,  sulphate  of  lime,  chloride  of  calcium,  and  the  like, 
are  always  found  in  sea-water. 


AQUEOUS     ROCKS. 


53 


lion  of  solid  carbonate  of  lime  is  deposited.  The  same  drop  also  deposits  an- 
other minute  portion  of  calcareous  matter  on  the  spot  upon  which  it  falls, 
and  as  the  drops  collect  on  nearly  the  same  spot  for  a  long  period  of  time,  a 
dependent  mass  like  an  icicle  is  formed  from  the  roof  of  the  cavern — the 
Btalactite ;  while  another  incrustation  gradually  rises  up  from  the  floor  be- 
neath— the  stalagmite.  In  the  process  of  time  the  two  may  meet,  and  thus 

FIG.  19. 


form  a  continuous  column.  Fig.  19  represents  the  appearance  of  these  depo- 
sitions in  the  Mammoth  Cave  of  Kentucky.  Vertical  sheets  of  the  same 
material  may  also  be  built  up,  as  when  the  water  drips  from  a  long  joint  or 
fissure  in  the  roof.  The  limestone  thus  formed  is  commonly  white  or  pale 
yellow,  often  fibrous,  and  when  thm,  semi-transparent  and  crystalline. 

Stalactites  may  also  often  be  observed  under  vaults  and  arches,  especially 
if  the  stone  of  which  they  are  constructed  is  limestone. 

64.  Calcareous  Tufa,  or  Travertine  is  a  deposit  anaf^ 
ogous  to  stalactite,  formed  at  the  margins  or  bottoms  of 


QUESTION. — What  Is  calcareous  tufa,  or  travertine  ? 


54          FIEST     PRINCIPLES     OF     GEOLOGY. 

springs  or  rivers,  or  wherever  water  holding  carbonate  of 
lime  in  solution  is  subjected  to  evaporation. 

Travertine  forms  beds  of  limestone  of  considerable  extent,  which  is  often 
crystalline,  and  sufficiently  compact  to  be  used  for  architectural  purposes. 
The  Colosseum  at  Rome  and  the  walls  and  temples  at  Psestum  are  built  of 
stone  thus  formed.*  Thermal  springs  produce  travertine  most  abundantly, 
and  at  a  locality  in  the  vicinity  of  Rome  a  layer  of  this  rock,  thirty  feet  in 
thickness,  has  been  formed  in  twenty  years.  It  is  also  deposited  by  springs 
of  ordinary  temperature,  and  in  some  localities  in  great  quantity,  as  at  New- 
Lebanon,  Chittenango  and  Sharon  Springs,  in  the  State  of  New  York.  At  the 
last-mentioned  springs  a  mass  of  tufa  has  been  formed,  which  contains  upward 
of  200,000  cubic  yards  of  rock. 

The  waters  of  some  springs  contain  so  large  a  proportion  of  calcareous 
matter  when  they  first  issue  from  the  earth,  and  deposit  it  so  readily  on  ex- 
posure to  the  air,  that  advantage  is  often  taken  of  the  circumstance  to  obtain 
incrustations  of  sticks,  leaves,  baskets,  birds'  nests,  etc.  Fig.  20  is  a  repre- 
sentation of  a  twig  of  wood  thus  incrusted. 


At  the  Baths  of  San  Fillipo,  in  Tuscany,  Italy,  the  preparation  of  casts  in 
this  manner  from  molds,  las-reliefs  and  medallions,  constitutes  a  regular  busi- 
ness. 

Very  beautiful  impressions  of  a  great  variety  of  leaves  in  travertine  are 
abundant  at  Sharon,  N.  Y.,  and  large  masses  of  incrusted  moss  are  common 
at  Niagara  and  Genesee  falls;  while  in  the  vicinity  of  Caledonia,  Livingston 
Co.,  N.  Y.,  the  incrustations  of  organic  structures  are  so  abundant  that  they 
are  used  in  the  construction  of  walls  and  fences. 

65.  Fresh-Water  Limestones, — This  name  has  been  given 
to  a  class  of  limestones  which  have  evidently  been  depos- 
ited at  the  bottom  of  fresh- water  lakes. 

Some  varieties  resemble  travertine  in  their  appearance,  but  in  general  they 

QUESTIONS. — Give  some  examples  of  its  formation.  What  are  the  fresh-water  lime- 
stones ? 

*  The  name  "travertine"  is  derived  from  the  river  Tiber,  and  simply  means  "  Tiber- 
atone." 


MARINE     LIMESTONES.  55 

appear  to  be  the  result  of  the  deposition  of  a  calcareous  mud  (the  product  of 
the  disintegration  of  shells  and  the  wear  of  previously  existing  limestones) 
mingled  with  clay  and  the  detritus  of  other  rocks.  In  some  instances  the 
proportion  of  clay  present  is  sufficient  to  convert  them  into  marls.  Fresh- 
water limestones  are  usually  rich  in  organic  remains — shells,  bones  of  ani- 
mals and  the  leaves  and  stems  of  plants. 

66.  Marine  Limestones, — Limestones  of  the  class  of  tra- 
vertines, tufas  and  fresh-water  limestones  constitute,  how- 
ever, but  a  veiy  small  proportion  of  the  great  deposits  of 
carbonate  of  lime  distributed  throughout  the  earth's  crust ; 
and  most  of  the  calcareous  rocks,  from  the  abundant  re- 
mains of  marine  animals,  corals,  shells,  etc.,  contained  in 
them,  appear  to  have  been  formed  beneath  the  waters  of 
the  ocean,  and  are,  therefore,  termed  "  marine  limestones/' 

Geologists  and  chemists  are  not  fully  agreed  as  to  the  manner  in  which 
these  immense  deposits  of  marine  limestones  have  originated.  That  carbon- 
ate of  lime  has  been  deposited  from  solution  in  sea- water,  at  the  bottom  of  the 
ocean,  like  travertine,  in  consequence  of  extensive  evaporation,  is  obviously 
improbable.  The  quantity  of  carbonate  of  lime  present  in  sea-water  is,  more- 
over, comparatively  small.  Some  geologists,  therefore,  have  advocated  a 
theory  that  lime  is  an  organic  product,  and  that  the  marine  animals  and  plants, 
which  secrete  carbonate  of  lime  abundantly,  produce  it  by  the  agency  of  vi- 
tality from  other  and  more  simple  substances.  Such  a  supposition  is,  how- 
ever, at  variance  with  every  principle  of  chemical  philosophy,  and  at  present 
has  few  or  no  supporters. 

Other  geological  writers  are  of  the  opinion,  that  whatever  may  have  been 
the  condition  of  lime  as  an  original  constituent  of  the  earth's  crust,  all  the 
marine  limestones  have  been  formed  by  the  intervention  of  the  powers  of  or- 
ganic life,  which,  as  manifested  in  marine  animals  and  plants,  have  abstracted 
the  carbonate  of  lime,  particle  by  particle,  from  the  sea- water,  and  by  solidify- 
ing it,  have  enabled  it  to  form  compact  rock-masses.*  This  hypothesis  finds 


QUESTIONS. — "What  evidence  have  we  that  the  majority  of  the  limestones  are  of  marine 
origin  ?    What  theories  of  their  origin  have  been  adopted  ? 


*  ".When  -we  consider  the  vast  quantity  of  carbonate  of  lime  which  is  daily  and  hourly 
being  separated  to  form  the  solid  parts  of  animals,  and  remember  that  the  operation  goes 
on  in  wide  tracts  of  open  water  as  well  as  on  the  sea-shore  to  a  far  greater  degree  than  is 
possible  on  land ;  that  every  race  of  molluscs,  crustaceans  and  zoophytes,  inhabiting 
shells,  or  building  coral  reefs,  or  constructing  other  stony  skeletons  and  dwelling-places, 
secretes  a  quantity  of  this  material  from  the  sea-water  and  renders  it  permanent  in  a 
solid  form  : — when  we  remember,  too,  that  the  quantity  secreted  by  each  individual  dur- 
ing its  brief  existence  is  almost  always  greater  in  proportion  as  the  animal  is  smaller  and 


56          FIRST     PRINCIPLES     OF     GEOLOGY. 

strong  support  in  the  fact  that  nearly  all  the  stratified  limestones  abound  in 
the  fossil  remains  of  marine  organisms,  and  in  many  instances  the  entire  mass 
of  rock  over  wide  areas  is  wholly  composed  of  corals  and  shells  compacted  to- 
gether by  a  calcareous  mud  or  cement  derived  from  the  waste  of  analogous 
materials. 

Similar  marine  limestones,  furthermore,  are  now  in  process  of  formation  on 
an  extensive  scale  in  most  tropical  seas,  which  abound  with  shells  and  corals. 
In  the  vicinity  of  Florida,  Hayti  and  the  Bermudas,  especially,  the  sea  is 
loaded  with  fine  calcareous  matter,  the  product  of  the  action  of  the  waves  on 
coral  reefs  and  dead  shells;  and  these  fine  particles  of  lime,  acting  as  a 
cement  between  larger  fragments  of  shells  and  corals,  gradually  produce  hard, 
compact  limestones.  Eecent  investigations  by  Prof.  Agassiz  have  shown, 
that  in  this  way  the  whole  of  the  southern  portion  of  the  peninsula  of  Florida, 
extending  from  the  Atlantic  to  the  Gulf  of  Mexico,  and  including  the  district 
known  as  the  "  Everglades,"  has  been  built  up  from  the  ocean.* 

From  these  and  similar  facts  and  observations  (which  will  be  noticed  more 
in  detail  hereafter),  we  are  able  to  form  tolerably  accurate  notions  respecting 
the  origin  of  many  marine  limestones — making  allowance,  at  the  same  time,  for 
the  changes  which  they  have  undergone  in  texture  since  their  formation  and 
elevation  above  the  ocean,  from  the  pressure  of  overlying  strata  of  other  rocks 
— from  the  denuding  and  chemical  action  of  rain-water  and  the  atmosphere — 
or  from  the  contiguity  of  rocks  of  an  igneous  origin. 

Recent  investigations,  conducted  by  Mr.  T.  S.  Hunt  of  the  Canadian  Geolog- 
ical Survey,  have  also  rendered  it  probable  that  some  of  the  marine  limestones 
have  had  a  direct  chemical  origin.f 

67.  Magnesian  Limestones  (carbonates  of  lime  and  mag- 
nesia) occur  abundantly  in  the  earth's  crust.  They  are 

its  life  shorter,  and  at  the  same  time  that  the  number  of  individuals  is  then  largest  and 
the  multiplication  of  the  species  most  rapid,  little  astonishment  will  be  felt  at  the  vast 
accumulations  thus  made  in  the  course  of  years,  or  the  result  thus  produced  upon  the 
mass  of  solid  matter  in  the  earth's  crust." — Ansted. 

*  On  the  coast  of  the  Antilles  these  formations  of  the  present  ocean  contain  articles  of 
pottery  and  other  objects  of  human  industry,  and  in  Guadaloupe  even  human  skeletons 
of  the  Carib  tribes.  In  Hayti  similar  formations,  called  by  the  negroes  Maf  onnerie  bon 
Dieu  (God'  a  Masonry)  extend  inland  thirty  miles,  and  rise  to  a  height  of  upwards  of  a 
thousand  feet  above  the  present  sea-level. 

t  Mr.  Hunt  has  shown  that  the  addition  by  degrees  of  dilute  solutions  of  bi-carbonate 
of  soda  to  liquids  which,  like  sea-water,  contain  both  salts  of  lime  and  magnesia,  causes 
the  separation  and  precipitation  of  the  whole  of  the  lime  present  as  carbonate,  and  then 
gives  rise  to  solutions  of  bi-carbonate  of  magnesia,  which  separates  from  concentrated 
solutions  as  a  hydrous  carbonate.  The  bi-carbonate  of  soda  is,  at  the  same  time,  con- 
verted into  chloride  of  sodium  (common  salt).  We  have  thus  an  explanation  of  several 
points  which  geologists  have  hitherto  found  difficulty  in  accounting  for,  viz.,  the  produc- 
tion of  some  marine  limestones,  of  the  magnesian  limestones  (carbonates  of  lime  and 
magnesia),  and  in  part  of  sea-salt;  the  bi-carbonate  of  soda,  the  agent  in  producing  these 
changes,  being  derived  from  the  decomposition  of  feldspathic  rocks  and  carried  into  the 


MAGNESIAN     LIMESTONES. 


57 


supposed  to  have  been  formed  through  the  chemical  de- 
composition of  the  salts  of  lime  and  magnesia  contained  in 
sea-water  and  to  have  been  deposited  at  the  bottom  of  an 
ancient  ocean. 

Magnesia  is  one  of  the  most  abundant  of  the  mineral  constituents  found 
in  sea- water,  but  does  not  enter  to  any  extent  into  the  composition  of  the  hard 
parts  of  marine  animals — corals,  shells,  etc. 

Magnesian  limestones  are  very  variable  in  their  lithological  characters.  In 
general  they  are  inferior  in  compactness  and  fineness  of  texture  to  pure  car- 
bonate of  lime,  and  are  commonly  of  a  yellowish-brown  or  gray  color,  with 
very  frequently  a  pearly  luster.  Some  varieties  are  earthy  and  friable,  while 
others  admit  of  being  split  into  long,  thin  slabs,  which  are  sometimes  flexible, 
and  constitute  the  so-called  "  elastic  marble."*  Many  magnesian  limestones 
have  also  a  curious  concretionary  structure. 

Silicious  Sinter.— This  name  (Ger.  sintern,  to  drop)  is 
given  to  aqueous  deposits  of  silica,  most  frequently  ob- 
served in  the  vicinity  of  thermal  (warm)  springs. 

Thus  at  the  Geysers,  or  hot  springs  of  Iceland,  a  deposit  about  a  mile  in 
diameter  and  twelve  feet  thick  occurs ;  and  at  the  hot  springs  of  the  Azores 
elevations  of  silicious  matter  thirty  feet  in  height  have  been  formed. 

68.  Infusorial  Earth, — Microscopic  investigations  have 
shown  that  many  accumulations  of  stratified  earths  and 
rocks  are  almost  wholly  composed  of  the  mineral  struc- 
tures— shells  or  skeletons — of  minute  animal  or  vegetable 


QUESTIONS. — What  is  said  of  the  distribution  and  formation  of  the  magnesian  lime- 
stones?   What  of  their  character  ?    What  is  silicious  sinter  ?    What  is  infusorial  earth  f 


sea  by  washings  from  the  land.    The  decomposition  of  the  feldspathic  rocks  has  further 
resulted  in  the  formation  of  clays  and  clay-slates. 

The  following  analysis  by  Von  Bibra  shows  the  mineral  constituents  of  the  waters  of 
the  North  Atlantic: 

Solids  in  100  parts  of  water 3.47  per  cent. 

Chloride  of  sodium  (common  salt)  in  100  parts  of  solids          76.05 


9.00 
4.00 
1.15 
4.GO 
5.20 
traces. 
Carbonate  of  lime,  fluorine,  iron,  silica,  phosphoric  acid,  ammonia,  baryta,  strontia, 

manganese  and  iodine  also  exist  to  some  extent  in  sea-water. 
*  The  magnesian  limestone  found  at  New  Ashford,  Berkshire  county,  Mass.,  when 

sawed  into  slabs  exhibits  a  very  high  degree  of  flexibility. 


Chloride  of  magnesium 
Chloride  of  potassium 
Bromide  of  sodium 
Sulphate  of  lime  (gypsum) 
Sulphate  of  magnesia  (Epsora  salts) 
Sulphate  of  potassa 


58  FIRST     PRINCIPLES     OF     GEOLOGY. 

organisms,  which,  from  the  circumstance  that  similar  forms 
are  readily  obtained  from  most  stagnant  infusions  of  vege- 
table matter,  have  been  called  infusoria* 

The  composition  of  these  shields  or  casings  is  frequently  pure  silica;  but 
they  may  be  composed  of  lime  or  even  oxyd  of  iron — these  substances  being 
secreted  by  the  organism  from  water  holding  silica,  lime  or  oxyd  of  iron  in 
solution. 

The  dimensions  of  the  infusorial  structures  are  so  minute,  that  the  greater 
portion  require  the  aid  of  a  microscope  to  establish  the  fact  even  of  their  ex- 
istence; many  complete  individuals  being  less  than  l-3000th  of  an  inch  in 
length.  According  to  Ehrenberg  (a  German  microscopist  who  has  made  this 
subject  a  speciality)  35,000  millions  of  some  species  would  be  requisite  to  oc- 
cupy the  space  of  a  single  cubic  inch,  and  the  late  Prof.  Bailey,  of  West  Point, 
estimated  the  number  of  separate  structures  in  a  cubic  inch  of  infusorial  earth 
from  Maidstone,  Vermont,  at  15,625,000,000. 

Notwithstanding,  however,  the  almost  inconceivable  minuteness  of  these 
organisms,  the  rock  deposits  formed  and  now  forming  of  their  remains  are  of 
great  extent  and  thickness.  At  Richmond,  Virginia,  beds  of  silicious  infu- 
sorial earth  occur  from  twenty  to  fifty  feet  in  thickness,  and  deposits  of  less 
magnitude  may  be  found  in  almost  all  sections  of  the  United  States.  In 
Germany  beds  a  hundred  miles  in  extent  have  been  noticed,  with  a  thickness, 
in  some  localities,  of  upward  of  sixty  feet. 

Fig.  21  is  a  magnified  representation  of  some  of  the  microscopic  structures 
most  common  in  the  infusorial  earths  of  Richmond,  Va.f 

QUESTIONS.— What  is  the  composition  of  the  so-called  infusoria  ?  What  are  their  di- 
mensions ?  What  is  said  of  their  distribution  ? 


*  The  term  infusoria  was  originally  used  as  a  general  designation  for  a  great  variety 
of  microscopic  organisms,  which  were  also  regarded  as  animalcules  (little  animals).  Re- 
cent investigations,  however,  have  shown  that  many  of  the  so-called  "infusoria"  are  not 
animals,  but  microscopic  plants  belonging  to  the  natural  order  Algae  ; — as,  for  example 
the  diatomacece,  which  are  simply  vegetable  cells  c;o  covered  with  silica  that  they  retain 
their  structure  permanently,  and  have  thus  been  enabled  to  constitute  geological  deposits 
of  great  extent  and  thickness.  According  to  the  most  recent  zoological  classification, 
the  term  infusoria  is  now  applied  only  to  certain  forms  of  animalctilae  which  constitute 
the  highest  class  of  the  Protozoa,  which  last  is  the  name  given  to  the  first  or  lowest  divi- 
sion of  the  animal  kingdom.  According  to  the  latest  zoological  authorities,  moreover,  there 
are'no  fossil  infusoria,  but  the  microscopic  organisms  usually  designated  by  this  name 
include  a  variety  of  animal  and  vegetable  species,  e.  g.,  Foraminifera,  Diatomacea?,  etc. 

t  Fig.  1  is  termed  a  navicula  (like  a  little  boat) ;  1  a,  a  side  view ;  6  and  6  a  represent  cu- 
rious saucer-shaped  shells  or  discs,  having  surfaces  elaborately  ornamented  with  hex- 
ogonal  spots  disposed  in  curves,  presenting  some  resemblance  to  the  engine-turned  case 
of  a  watch,  as  especially  shown  in  Fig.  2,  which  is  a  small  segment  of  a  disc  highly 
magnified.  These  discs  vary  in  size  from  l-100fch  to  1-1 000th  of  an  inch  in  diameter,  and 
are  named  coscinodiscus  (sieve-like  disc).  3  and  3  a  are  jointed  forms,  called  Gallion- 
ella ;  4  and  5  are  circular  bodies  with  five  or  six  lines  radiating  from  the  center  like  the 
sppkes  of  a  wheel,  and  hence  termed  Actinocylus, 


GYPS^UM     AND      ROCK-SALT. 


59 


69.  Sulphate  of  Lime  (gypsum)  and  Rock-Salt  (chloride 
of  sodium)  both  occur  in  sufficient  abundance  in  numerous 
localities  to  merit  the  designation  of  rock-masses. 

Gypsum  is  found  under  various  conditions ;  sometimes  as  regular  beds  of 
considerable  extent  and  thickness;  sometimes  as  irregular  concretionary 
masses,  and  not  unfrequently  in  the  form  of  veins  or  seams  in  other  rocks. 
Alabaster  (so  called  from  the  town  Alabastron  in  Egypt)  is  a  compact  variety 
of  gypsum.  Selenite  is  a  crystalline  and  often  transparent  variety. 

Rock-salt  commonly  occurs  in  imperfectly  crystalline,  irregularly  bedded 
masses,  associated  with  various  clays  and  marls,  and  very  frequently  with 
beds  of  gypsum,  as  if  the  salt  and  gypsum  had  both  been  deposited  at  nearly 
the  same  time  and  under  the  same  circumstances.  At  Wurtemberg,  Germany, 
beds  of  salt  occur  in  lirnsstone.  In  England  bed-like  masses  of  salt  are  often 
sixty  to  ninety  feet  thick,  thinning  out  apparently  in  all  directions,  and  thus 
assuming  the  form  of  large  cakes.  A  deposit  of  rock-salt  near  Cracow,  in 
Poland,  is  estimated  to  be  500  miles  in  length,  twenty  broad,  and  not  less  than 
1,200  feet  thick.  As  a  mineral,  rock-salt  is  sometimes  perfectly  pure  and  white, 
but  in  most  cases  it  is  obtained  in  the  condition  of  an  impure  chloride  of  so- 
dium, in  masses  of  a  dirty  red  color,  and  with  little  of  that  transparency  and 
brilliancy  which  characterize  the  pure  mineral. 

70.  Origin  of  Sulphate  of   Lime    and  Rock-Salt. — Sulphate 
of  lime  and  rock-salt  are  generally  believed  to  have  been  deposited  from  sea- 

QTJEBTIONB.— What  is  said  of  the  distribution  of  sulphate  of  lime  and  rock-salt  ?  What 
is  gypsum  ?  Under  what  circumstances  does  it  occur  ?  What  are  some  of  its  varieties  ? 
In  what  condition  is  rock-salt  found  ? 


60         FIRST     PRINCIPLES     OF      GEOLOGY. 

water,  of  which  they  arc  abundant  constituents.  This  deposition  may  have 
been  the  result  of  a  gradual  dessication  of  limited  areas  of  salt-water,  alter- 
nately cut  off  and  placed  in  connection  with  the  ocean,  or  of  direct  chemical 
action.  A  precipitation  of  salt  from  the  ocean  itself  as  the  result  of  evapo- 
ration, probably  never  occurs ;  but  in  shallow,  isolated  lakes,  where  the  water 
is  entirely  saturated  with  salt,  as  in  some  of  the  salt  lakes  of  Asiatic  Rus- 
sia, the  precipitation  of  rock-salt  from  evaporation  may  be  observed.  Salt 
thus  deposited  is  generally  interstratified  with  earthy  sediment,  and  the  like 
condition  of  many  beds  of  salt  in  geological  formations  would  indicate  that 
the  latter  may  have  been  formed  under  similar  circumstances.  The  great 
thickness,  however,  of  other  deposits  of  rock-salt,  and  the  comparative  purity 
and  homogeneity  of  their  mass,  would  seem  to  imply  the  operation  of  more 
active  forces. 

71.  Bog  Iron  Ore, — This  name  is  given  to  a  very  common 
ore  of  iron   (hydrated  peroxyd  of  iron)   deposited   from 
waters  holding  oxyd  of  iron  in  solution. 

Oxyd  of  iron  is  only  slightly  soluble  in  pure  water,  but  waters  which  con- 
tain organic  acids — the  products  of  decomposing  vegetable  matter — dissolve 
out  oxyd  of  iron  freely  from  the  earth  and  rocks  with  which  it  (the  water) 
comes  in  contact.  The  iron  which  thus  passes  into  solution  is,  after  a  time. 
by  exposure  to  the  air  and  a  continuance  of  the  decomposing  action,  precipi- 
tated from  the  water  in  an  insoluble  form,  and  in  this  way  deposits  of  yellow, 
earthy  oxyd  of  iron  are  formed,  of  varying  extent  and  thickness.  From  the 
circumstance  that  such  deposits  are  formed  most  frequently  at  the  bottom  of 
bogs  and  marshes,  they  have  received  the  name  of  "  bog  iron  ore."  The  ir- 
ridescent  film  which  may  be  often  noticed  on  the  surface  of  stagnant  waters 
is  composed  of  oxyd  of  iron  passing  from  a  state  of  solution.  Many  speci- 
mens of  "  bog  iron  ore,"  when  examined  under  the  microscope,  will  appear  to 
be  almost  entirely  composed  of  the  shields  of  infusorial  organisms. 

72.  Hydrate  of  Manganese  is  frequently  deposited  from 
shallow  pools  and  lakes  of  fresh- water  in  the  form  of  an 
earthy  oxyd,  technically  called  "  load"  or  "  ivadd." 

The  blackening  of  stones  and  pebbles  in  the  beds  of  streams  flowing  over 
silicious  rocks  is  in  a  great  measure  due  to  a  thin  incrustation  of  oxyd  of 
manganese — a  phenomenon  which  may  be  especially  noticed  in  most  of  the 
mountain  streams  of  New  England. 

73.  Coal,  which  is  essentially  of  organic  origin,  is  a  rock 


QUESTIONS. — What  is  said  of  the  origin  of  sulphate  of  lime  and  rock-salt  ?  What  is 
bog  iron  ore  ?  How  is  it  formed  ?  What  is  said  of  the  distribution  of  manganese  ?  What 
is  coal? 


METAMORPHIC      ROCKS.  61 

generally  familiar  in  its  aspect  and  nature.  It  occurs  in 
the  earth  in  beds  or  seams,  associated  or  interstratified  with 
shales,  indurated  clays,  limestones  and  earthy  ores  of  iron. 

Lignite,  bitumen,  asphdltum  and  the  like,  are  mineral  products  of  organic 
origin  allied  to  coal.  Their  composition,  character  and  distribution  will  be 
considered  in  a  subsequent  chapter. 


CHAPTER    VI. 

VARIETIES  AND  LITHOLOGrlCAL  CHARACTERS  OP  THE 
METAMORPHIC  ROCKS. 

74.  The  term  "  Metamorphic,"  when  applied  to  rock 
masses,  signifies,  as  has  been  already  stated,  that  their 
original  structure,  texture  and  chemical  condition,  have 
undergone  some  internal  change  or  metamorphosis. * 

As  there  is,  however,  scarcely  one  of  the  infinite  variety  of  accumulations 
Of  mineral  matter  constituting  the  earth's  crust,  which  has  not  been  changed 
to  a  greater  or  less  degree  since  its  formation,  by  chemical  or  mechanical 

QUESTIONS. — What  is  the  signification  of  the  term  "  metamorphic,"  as  used  in  geology  ? 


*  Professor  Studer,  a  celebrated  Swiss  chemist  and  geologist  (Edin.  New  Phil.  Journ., 
Jan.,  1848),  defines  metamorphism  as  follows: — "In  its  widest  sense,  mineral  meta- 
morphism  means,  every  change  of  aggregation,  structure,  or  chemical  condition  which 
rocks  have  undergone  subsequently  to  their  deposition  and  stratification,  or  the  effects 
which  have  been  produced  by  forces  other  than  gravity  and  cohesion.  There  fall  under 
this  definition  the  discoloration  of  the  surface  of  black  limestone  by  the  loss  of  carbon ; 
the  formation  of  brownish -red  crusts  on  rocks  of  limestone,  sandstone,  many  slate  stones, 
granite,  etc.,  by  the  decomposition  of  compounds  of  iron  finely  disseminated  in  the  mass 
of  the  rock ;  the  change  in  rocks  consequent  on  the  absorption  of  water  ;  and  the  crumbling 
of  many  granite  and  porphyries  into  gravel,  occasioned  by  the  decomposition  of  the  mica 
and  feldspar.  In  its  more  limited  sense,  the  term  metamorphic  is  confined  to  those 
changes  of  the  rock  which  are  produced,  directly  or  indirectly,  by  agencies  seated  in  the 
interior  of  the  earth.  In  many  cases  the  mode  of  change  may  be  explained  by  our 
physical  or  chemical  theories,  and  may  be  viewed  as  the  effect  of  temperature  or  of 
electro-chemical  actions.  Adjoining  rocks,  or  connecting  communications  with  the  in- 
terior of  the  earth,  also  distinctly  point  out  the  seat  from  which  the  change  proceeds. 
In  many  other  cases  the  metamorphic  process  itself  remains  a  mystery ;  and  from  the 
nature  of  the  products  alone  do  we  conclude  that  such  a  raetamorphic  action  has  taken 
place." 


62  FIRST     PRINCIPLES     OF     GEOLOGY. 

agencies,  it  is  obvious  that  a  classification,  founded  on  such  a  characteristic," 
must  of  necessity  be  exceedingly  general.  In  fact,  by  some  authorities, 
metamorphism  is  not  considered  as  affording  a  sufficient  basis  for  the  es- 
tablishment of  a  classification,  while  the  majority  of  geologists,  who  recognize 
it  as  such,  are  not  fully  agreed  as  to  its  limitations.  Some  geologists  even 
consider  granite  and  other  highly  crystalline  and  compact  rocks,  to  which  a 
direct  igneous  origin  is  usually  assigned,  as  truly  metamorphic,  or,  in  other 
words,  as  sedimentary  strata,  altered  under  the  influence  of  heated  water, 
or  water  holding  chemical  agents  in  solution.  These  views,  which  derive 
strong  support  from  the  results  of  recent  investigations,  are  not,  however, 
adopted  by  all  geologists,  and  in  the  present  work  we  shall  describe  only 
those  rocks  as  metamorphic  which  are  generally  believed  to  have  been  origin- 
ally deposited  as  sediments,  and  to  have  acquired  their  present  compact, 
crystalline,  or  semi-crystalline  character  through  the  subsequent  action  of 
various  chemical  or  mechanical  agencies. 

Under  such  restrictions,  the  following  rocks  may  be  enumerated  as  belong- 
ing to  the  class  metamorphic:  — 

CLAY,  or  ARGILLACEOUS  SLATE  ;  QUARTZ  KOCK,  or 
QUARTZITE  ;  HORNBLENDE  SCHIST  ;  TALCOSE  SCHIST  ; 
MICA  SLATE,  or  SCHIST;  G-NEISS  ;  ALTERED,  or 'META- 
MORPHIC LIMESTONES  ;  DOLOMITES,  or  CRYSTALLINE 
MAGNESIAN  LIMESTONES  ;  SERPENTINE. 

75.  Clay,  »or  Argillaceous  Slate  (common  slate,  as  it  is 
frequently  designated)  is  an  indurated,  compact  clay  rock. 

As  a  result  of  the  metamorphic  action  to  which  it  has  been  subjected,  it 
has  assumed  a  perfectly  "  fissile"  or  slaty  structure,  a  peculiarity  which  ren- 
ders some  varieties  especially  valuable  for  roofing  and  flagging  purposes.  The 
finer  sorts  are  also  used  for  writing- slates  and  slate-pencils,  and  to  some  ex- 
tent for  hones  and  whetstones.  The  prevalent  colors  of  clay  slate  are  a  dull 
blue,  red,  green,  purple,  gray  and  mottled.  It  passes,  by  insensible  grada- 
tions, into  hard,  crystalline  schists,  containing  quartz  and  mica,  on  the  one 
hand,  and  on  the  other  into  dull,  friable  shales,  or  even  into  unconsolidated 
clay.* 

Clay  slates,  containing  sulphuret  of  iron  (iron  pyrites),  tend  to  undergo  de- 
composition on  exposure  to  air  and  moisture ;  the  sulphur  of  the  sulphuret 

QUESTIONS.— What  is  said  of  a  classification  of  rocks  founded  on  such  changes?  What 
class  of  rocks  are  usually  termed  metamorphic  ?  Enumerate  them  ?  What  is  clay  slate  ? 

*  According  to  some  geologists,  clay  slate  is  the  only  rock  to  which  the  term  slate  prop- 
erly applies;  the  other  fissile  argillaceous  rocks  being  either  shales  or  schist. 


METAMORPHIC     ROCKS.  63 

of  iron  uniting  with  oxygen  to  form  sulphuric  acid,  which  subsequently  com- 
bines with  the  alumina  of  the  clay  to  form  sulphate  of  alumina.  This  latter 
product,  which  frequently  appears  on  the  surface  as  a  white  efflorescence,  and 
may  be  obtained  in  solution  by  washing,  is  practically  valuable  in  the  arts  for 
the  manufacture  of  alum,  and  the  slates  capable  of  yielding  it  by  decomposi- 
tion are  technically  known  as  alum  slates. 

76.  Quartz    Rock,    or    Quartzite,*  is  a  compact,  fine- 
grained, but  distinctly  granular  rock,  very  hard,  frequently 
brittle,  and  often  so  divided  by  joints  as  to  readily  split  in 
all  directions. 

Its  colors,  from  the  presence  of  oxyd  of  iron,  are  generally  of  some  shade 
of  yellow,  passing  into  dull  red  or  brown. 

"  "When  examined  with  a  lens  it  may  be  seen  to  be  made  of  grains,  which 
appear  sometimes  as  if  they  had  been  slightly  fused  together  at  their  edges 
or  surfaces,  and  sometimes  as  if  embedded  in  a  purely  silicious  cement. 
This  cementation  or  semi-fusion  of  the  grains  shows  at  once  that  it  is  a  sand- 
stone which  has  been  altered  or  indurated  by  the  action  either  of  heat  alone 
or  heat  and  water.  It  has  been  either  baked  or  steam-boiled." — JUKES. 

In  some  varieties  of  quartz  rock,  resulting  from  an  intermixture  with  horn- 
blende, talc,  mica,  or  clay  slate,  the  regular  stratification  is  often  apparent, 
but  in  other  cases  every  trace  of  a  mechanical  structure  seems  wanting. 

77.  Hornblende  Schist  (hornblende  rock)  consists  mainly 
of  hornblende,  with  varying  proportions  of  feldspar,  quartz, 
mica,  or  talc.     Its  color  is  usually  dark  green. 

78.  T  a  I  co  s  e  Schist . — The  characteristic  and  essential  con- 
stituent of  this  rock  is  talc,  associated  with  quartz,  and 
sometimes  with  mica,  feldspar,  hornblende,  and  limestone. 
Its  prevailing  color,  owing  to  the  abundance  of  the  talc, 
is  a  tint  of  green.     When  chlorite  is  found  in  the  place  of 
talc,  the  rock  is  termed  a  chloritic  schist. 

79.  Mica  Schist  (mica  slate)  consists  of  alternate  layers 
of  mica  and  quartz,  the  mica  predominating,  and  existing 

QUESTIONS.— What  is  the  characteristic  of  clay  slate  ?  What  are  alum  slates  ?  What 
is  said  of  quartz  rock,  or  quartzite  ?  What  are  the  characteristics  of  hornblende  schist  ? 
What  of  talcose  schist  ?  What  of  mica  schist  ? 


*  The  student  must  carefully  distinguish  between  pure  vein  quartz  and  the  quartz 
rock,  as  here  described.  The  former  has  a  highly  vitreous  or  flinty  texture,  is  never 
granular,  and,  although  sometimes  occuring  in  large  masses,  it  is  more  commonly  noticed 
in  the  form  of  veins,  or  segregations  in  other  rocks. 


64          FIRST     PRINCIPLES     OF     GEOLOGY. 

usually  in  the  form,  of  small  particles.     Its  color  is  gray, 
with  a  shining,  lustrous  appearance. 

Owing  to  the  facility  with  which  mica  schist  divides  into  large,  smooth 
slabs,  it  is  largely  used  for  flagging  purposes ;  and,  at  an  extensively  worked 
quarry  at  Bolton,  Conn.,  smooth  slabs  of  it,  eight  to  twelve  feet  square,  by 
one  and  a  half  to  three  inches  thick,  are  very  frequently  obtained.  Mica  schist 
is  one  of  the  most  common  rocks  of  the  metamorphic  series,  and  in  many 
localities  abounds  to  such  an  extent  in  the  minerals,  garnet  and  staurotide, 
that  the  latter  may  be  properly  regarded  as  constituents  of  it. 

80.  Gneiss,  in  its  purest  and  typical  form,  has  the  same 
component  elements  as  granite  :  viz.,  quartz,  feldspar  and 
mica,  with  an  occasional  admixture  of  hornblende,  all 
more  or  less  crystalline.  Unlike  granite,  however — which 
presents  a  confused  aggregation  of  crystals — the  constitu- 
ent minerals  of  gneiss  are  arranged  in  parallel  lines  or 
layers  ;  hence,  it  exhibits  a  marked  laminated  or  stratified 
appearance,  and  by  most  geologists  is  considered  as  really 
stratified. 

Sir  Chas.  Lyell  designates  gneiss  as  "stratified  granite;"  but  some  author- 
ities are  inclined  to  refer  the  peculiar  laminated  appearance  of  this  rock  to 
the  circumstances  under  which  it  cooled  from  a  state  of  fusion  rather  than  to 
an  original  aqueous  deposition  of  its  particles. 

Tig.  22  represents  the  appearance  and  structure  of  gneiss. 
FIG.  22. 


Some  varieties  of  gneiss,  by  an  indefinite  transition,  actually  pass  into 
granite;  others,  on  the  contrary,  can  scarcely  be  distinguished  from  mica 
schist,  which  last,  through  various  gradations,  may  pass  into  talcose  schist, 
and  even  into  dull,  earthy  clay  slate. 

The  contortions  of  the  layers  or  strata  of  gneiss  and  mica-schist  are,  in 
some  localities,  most  remarkable,  and  on  a  magnificent  scale.  (See  Fig.  23.) 
"Imagination,"  says  MacCulloch,  "can  scarcely  conceive  an  intricacy  of" flex- 

QTTESTIONB.— Describe  gneiss  ?  What  is  said  of  the  contortions  of  gneiss  and  mica 
slate. 


METAMOKPHIC     ROCKS. 


65 


ure  of  which  a  resemblance  cannot  be  found  in  the  gneiss  of  the  western 
islands  of  Scotland."  In  other  localities,  however,  the  same  rocks  are  dis- 
tinguished for  their  regularity  and  evenness. 

FIG.  23. 


81.  Distribution  of  the  above-described  Metamorphic 
Rocks , — The  metamorphic  rocks  above-described  are  widely  distributed, 
and  constitute  portions  of  most  of  the  older  mountain  chains  upon  the  surface 
of  the  globe — gneiss  and  mica  slate  being  perhaps  the  most  abundant  mem- 
bers of  the  series.  In  the  United  States,  these  rocks,  with  few  exceptions, 
form  the  White  Hills  of  New  Hampshire,  the  Green  Mountains  of  Vermont 
and  Western  Massachusetts,  and  the  Blue  Ridge  of  the  Southern  States. 
They  do  not,  however,  occupy  very  great  superficial  areas,  but  are  usually 
found  compressed  and  tilted  up  at  high  angles  (not  unfrequently  at  right 
angles  to  the  original  plane  of  their  deposition),  thus  producing  rugged  and 
abrupt  scenery.  They  are  everywhere  associated  with,  and  traversed  by, 
rocks  of  an  apparently  igneous  and  eruptive  origin,  such  as  granite,  syenite, 
and  porphyry— -which  agencies  would  also  appear  to  have  been  productive 
of  metamorphism,  upheavals  and  contortions. 

The  soils  resulting  from  the  decomposition  of  gneiss  and  mica  slate  are  not 
unfruitful ;  but  those  resulting  from  the  decomposition  of  clay  slate  are  cold 
and  clayey,  and  generally  unproductive. 

82.  Altered  or  Metamorphic  Limestones. — These  lime- 
stones, which  were  formerly  called  "primitive"  or  "prim- 
ary" limestones,  are  all  highly  compact  and  crystalline.* 

QUESTIONS. — What  is  said  of  the  distribution  of  the  above-described  metamorphic 
rocks?  What  of  their  influence  upon  the  surface  and  fertility  of  a  country?  What  are 
the  characteristics  of  the  metamorphic  limestones? 


*  The  existence  of  a  crystalline  texture  in  limestones  is  in  itself  no  proof  of  meta- 
morphism, in  the  ordinary  sense  of  the  term,  inasmuch  as  it  is  probable  that  some  lime- 
stones were  originally  formed  crystalline.  Thus,  many  parts  of  a  coral  reef  are,  even 
now,  crystalline  internally.  Carbonate  of  lime,  deposited  from  solution,  may  also  have  a 
crystalline  structure.  The  famous  statuary  marbles  of  Greece  and  Italy  are  metamorphic 
limestones. 


66 


FIEST     PRINCIPLES     OF     GEOLOGY. 


"  Some  are  pure  white,  fine-grained,  and  slightly  translucent,  and  from  their 
resemblance  in  color  and  texture  to  loaf-sugar  are  often  termed  ''saccharine." 
Such  limestones  work  freely  in  every  direction,  admit  of  fine  polish,  and  fur- 
nish the  finest  marbles  for  statuary  and  architectural  purposes.  Other  varie- 
ties  are  variously  colored,  coarsely  crystalline,  and  very  frequently  occur  iu 
thin  beds,  alternating  with  gneiss,  mica  schist  and  clay  slates. 

Metamorphic  limestones  occur  both  stratified  and  unstratified ;  when  as- 
sociated with  granite  -and  other  rocks  of  presumed  igneous  origin,  they  rarely 
exhibit  stratification ;  and  in  some  instances  the  limestone  exists  in  the  form 
of  veins,  as  if  it  had  been  injected  into  fissures  in  other  rocks  while  in  a  state 
of  fusion.*  Fig.  24  represents  veins  of  limestone  (a)  traversing  granite  (6) 
at  Gouverneur,  St.  Lawrence  Co.,  N.  Y.,  figured  by  Dr.  E.  EMMONS. 

FIG.  24. 


83.  Dolomite  is  a  highly  crystalline  aggregate  of  nearly 
equal  parts  of  carbonate  of  lime  and  carbonate  of  magnesia. 
It  is  believed  to  be  a  magnesian  limestone,  rendered  com- 
pact and  crystalline  through  the  joint  action  of  heat  and 
pressure. 

Dolomite  is  usually  white,  but  is  also  found  of  various  colors.  It  is  ex- 
tensively used  for  the  manufacture  of  lime  and  also  as  a  building  stone.  No 
lime  is  more  highly  prized  by  masons  than  that  made  from  the  close,  compact 
dolomite  of  Smithfield,  R.  I.,  and  at  Sing  Sing,  on  the  Hudson,  N.  Y.  As  a 
building  stone,  dolomite  ranks  among  the  best,  possessing  in  a  high  degree 

QUESTIONS. — What  is  dolomite?    What  are  its  characteristics  and  industrial  uses? 

*  Experiments  have  proved  that  limestone  (carbonate  of  lime),  when  subjected  to  pres- 
sure sufficient  to  prevent  the  escape  of  carbonic  acid,  may  be  entirely  fused,  and,  on  cool- 
ing, assumes  different  degrees  of  consolidation  and  crystallization,  according  to  the  pres- 


METAMORPHIC     ROCKS.  67 

the  properties  of  durability  and  ease  in  working.  It  forms  a  considerable 
part  of  the  white  marble  used  in  the  construction  of  the  Capitol  at  Washing- 
ton, and  the  Custom-houses  in  New  York  city,  and  Charleston,  S.  C.,  are  also 
constructed  of  it.* 

84.  Serpentine  (see  $16)  is  usually  classed  among  the 
igneous  and  eruptive  rocks,  but  the  most  recent  investiga- 
tions seem  to  establish  its  position  in  the  metamorphic 
series,  as  the  product  of  a  highly  altered  magnesian  lime- 
stone.     In  the  Canadian  Geological  Survey,  serpentines 
have  been  traced  to  a  gradual  termination  in  unaltered  beds- 
of  magnesian  limestone.     The  predominant  color  of  ser- 
pentine is  mottled  green.     The  finer  varieties  are  highly 
ornamental  and  susceptible  of  a  fine  polish.     When  as- 
sociated with  carbonate  of  lime  it  constitutes  the  "  verde 
antique"  marble. 

85.  Economic    Products    of    the   Metamorphic    Rocks. — 

The  economic  or  industrial  products  of  the  metamorphic  series  of  rocks  in  the 
United  States  embrace  the  different  varieties  of  slates,  many  of  the  marbles 
(especially  those  of  Vermont  and  Western  Massachusetts),  and  abundant  de- 
posits of  serpentine  and  steatite  (soapstone).  Pure  silicious  sand,  the  product 
of  the  decomposition  of  quartz  rock,  is  extensively  exported  from  Berkshire 
County,  Mass.,  for  the  manufacture  of  the  finest  varieties  of  glass.  Graphite, 
or  plumbago,  a  natural  variety  of  carbon,  largely  employed  for  writing-pen- 
cils, for  crucibles,  polishing,  etc.,  is  mainly  found  associated  with  meta- 
morphic rocks.  Gold  is  widely  distributed  in  these  rocks,  especially  in 
talcose  schists,  in  the  Southern  States,  along  the  Green  Mountain  range  of 
Vermont,  and  throughout  Canada ;  deposits  of  ores  of  iron  and  zinc  are  also 
not  unfrequent.  The  diamond,  beryl,  rock-crystal,  garnet,  zircon,  and  many 
other  precious  stones,  are  found  in  this  system,  either  embedded  in  the  strata 
themselves,  or  in  veins  that  traverse  them.  Neither  gneiss,  mica  slate,  or 
talcose  slate,  yield  very  elegant  building  materials ;  some  varieties  of  gneiss, 
however,  split  with  facility  into  huge  blocks,  and,  being  very  durable,  are 
extensively  employed  for  massive  constructions,  as  piers,  breakwaters,  etc. 

QUESTIONS.— What  is  serpentine?  What  is  verde  antique  marble?  What  are  the 
economic  products  of  the  metamorphic  rocks  ? 

•  In  England  dolomite  has  proved  so  excellent  and  durable  a  stone  that  a  variety  of  it 
was  selected  by  a  government  commission  as  the  best  material  in  the  kingdom  for  con- 
structing the  new  Houses  of  Parliament.  The  choir  of  Southwell  Church,  which  was 
built  of  this  variety  of  stone  in  the  twelfth  century,  was  found  by  the  commissioners  to 
be  in  so  perfect  a  state  that  "  the  moldings  and  carved  enrichments  were  as  sharp  as 
when  first  executed." 


68         FIEST     PRINCIPLES     OF     GEOLOGY. 


TABULAR. CLASSIFICATION  OF  ROCKS. 

86.  The  following  table  exhibits  the  principal  varieties 
of  rocks,  arranged  in  accordance  with  the  foregoing  classi- 
fication : 

IGNEOUS    BOOKS. 

VOLCANIC. 

TBACHTTIO  LAY  AS  (Trachytes).  PUMICE. 

AUGITIC  LAVAS.  SCORLE. 

OBSIDIAN.  VOLCANIC  TUFT. 

TRAPPEAN. 

BASALT.  DIORITES. 

GREENSTONE.  DOLERITES. 

PORPHYRY.  AMYGDALOID. 

CLAYSTONE.  TRAP  TUFF. 

GRANITIC. 

GRANITE.  GRAPHIC  GRANITE. 

SYENITE.  •  PORPHYRITIC  GRANITE. 

HYPERSTHENE  ROCK.  PROTOGENE. 

AQUEOUS  ROCKS. 
MECHANICALLY    FORMED. 

ALLUVIUM.  SAND. 

DRIFT,  OR  DILUVIUM.  CLAY,  MUD. 

SOIL.  SANDSTONE. 

GRAVEL.  MARL. 

CONGLOMERATE  AND  BRECCIA.  LOAM. 

SHALE.  SLATE. 

AQUEOUS    ROCKS. 
OP  CHEMICAL    OR    ORGANIC  ORIGIN. 

STALACTITE  AND  STALAGMITE.  COAL,  LIGNITE. 

CALCAREOUS  TUFA,  OR  TRAVERTINE.  SILICIOUS  SINTER. 

FRESH  WATER  LIMESTONES.  INFUSORIAL  EARTHS. 

MARINE  LIMESTONES.  ROCK-SALT. 

MAGNESIAN  LIMESTONES.  GYPSUM  (Sulphate  of  Lime). 

BOG-IRON  ORE.  HYDRATE  OF  MANGANESE  (Wadd). 
BITUMEN,  ASPHALTUM. 


STRUCTURE    AND   RELATION    OF    ROCKS.       69 

METAMORPHIC    ROCKS. 

CLAY,  OR  ARGILLACEOUS  SLATE.  TALCOSE  SCHIST. 

QUARTZ  ROCK,  OR  QCTARTZITE.     „  MICA  SLATE,  OR  SCHIST. 

HORNBLENDE  SCHIST,  OR  HORNBLENDE  ROCK.  GNEISS. 

METAMORPHIC  OR  ALTERED  LIMESTONES.  DOLOMITE. 
SERPENTINE. 


CHAPTER    Y 1 1 . 

STRUCTURE,    MECHANICAL  DISPLACEMENT,  AND    RELATIONS 
OF  ROCKS. 

87.  Having  described  the  varieties  and  lithological  cha- 
racters of  the  principal  rock-masses  which  enter  into  the 
composition  of  the  crust  of  the  globe,  we  come  next  to 
consider  the  actual  state  in  which  we  find  them  ;  or,  in 
other  words,  their  structure,  position  and  mutual  relations, 
and  also  the  disturbances  to  which  they  have  been  sub- 
jected. 

This  department  of  geology,  which  by  some  authors  is 
termed  "Petrology"  (the  study  of  rock-masses],  is  founded 
on  observations  which  can  be  made  only  "  in  the  field," 
and  on  an  extensive  scale. 

88.  Stratification  and  Lamination. — The  aqueous  rocks,  in 
general,  as  has  been  already  stated,  are  characterized  by  the  arrangement  of 
their  constituent  materials  into  strata  and  laminae  ;  the  former  designation 
being  applied  to  indicate  distinct  beds,  or  wide,  tabular  masses  of  rock,  com- 
pletely and  naturally  separated  from  each  other ;  while  the  latter  refers  to 
the  more  minute  subdivisions  or  layers  of  which  a  bed  is  made  up,  and  which 
may,  or  may  not  be  separable.  In  short,  the  laminae  bear  the  same  relation 
to  a  single  bed  or  stratum  that  the  latter  does  to  a  whole  series  of  beds,  or 
strata. 

A  careful  examination  of  these  beds  or  layers  reveals  at 
once  their  origin  and  the  history  of  the  rock  formation  of 
which  they  constitute  a  part.  Thus,  each  little  separate 
layer  was  obviously  the  result  of  a  separate  act  of  deposi- 

QUESTIOJT. — What  distinction  do  geologists  make  between  stratification  and  lamination  ? 


70         FIRST     PRINCIPLES      OF     GEOLOGY. 

tion  of  earthy  sediment  from  suspension  in  water — the  in- 
terval of  time  between  the  successive  acts  of  deposition 
being  distinct,  but  not  so  far  prolonged  as  to  allow  of  the 
consolidation  of  one  layer,  before  the  next  was  deposited 
upon  it.  The  whole  set  of  laminae,  therefore,  adhere  to- 
gether so  as  to  form  one  bed,  which  now,  as  rock,  may  be 
quarried  and  lifted  in  single  blocks.0  The  cause  of  the 
interruptions  in  the  deposition  of  the  sediment  which  have 
produced  laminas  we  may  conceive  to  have  been  periodical 
floods,  frequent  changes  in  the  force  of  currents,  successive 
tides,  or  other  like  agencies,  which,  in  some  instances,  re- 
newed the  supply  of  material,  and  in  others  deflected  it, 
or  suspended  its  settlement. 

If,  on  the  other  hand,  the  interruptions  between  the  acts 
of  deposition  were  so  far  prolonged  as  to  allow  a  mass 
of  laminated  material  to  consolidate  to  a  greater  or  less 
extent,  it  is  obvious  that  there  would  be  a  want  of  coher- 
ence between  it  (i.  e.,  the  hardened  material)  and  the  sedi- 
ment next  deposited  upon  it  ;  and  in  this  way  the  beds, 
which  we  call  strata,  would  be  formed  with  more  distinct 
lines  of  separation  between  them  than  exists  between  suc- 
cessive laminae. 

The  planes  of  lamination  and  of  stratification,  therefore,  both  mark  inter- 
ruptions in  the  act  of  sedimentary  deposition ;  but  the  intervals  between  the 
formation  of  successive  strata  were  undoubtedly  considerably  longer  than  be- 
tween successive  lamina.  In  some  instances,  where  the  particles  of  the  rock 
are  fine-grained  and  homogeneous,  it  is  exceedingly  difficult  to  distinguish 
the  planes  of  lamination  from  those  of  stratification.  In  such  cases,  the  whole 
mass  of  the  rock  may  have  been  deposited  rapidly  and  without  interruption  ; 
or  the  divisional  structure  may  have  been  obliterated  by  subsequent  pressure, 
or  other  metamorphic  agencies. 

Lamination  is  sometimes  parallel  with  the  planes  of  stratifications ;  some- 

QUESTIONS.— Explain  the  manner  in  which  strata  and  laminae  have  originated  ?  Are 
the  planes  of  lamination  always  parallel  to  those  of  stratification? 


*  "In  some  shales  the  coherence  between  the  laminae  is  very  slight,  and  they  may  bo 
pulled  asunder  by  the  hand  ;  but  in  others  it  is  more  complete,  and  in  some  quite  firm. 
In  some  laminated,  fine-grained  sandstones,  it  requires  almost  as  much  force  to  split 
them  along  the  lines  of  lamination  (or  with  the  (jrain,  to  use  a  common  term),  as  it  docs 
to  break  them  across."— Jukes. 


STRUCTURE  AND  RELATION  OF  ROCKS.   71 

times  inclined,  and  not  unfrequently  undulating  and  tortuous.  Fig.  25  repre- 
sents a  case  of  very  contorted  lamination,  figured  by  Prof.  Hitchcock,  in  a 
stratum  of  gneiss,  two  or  three  feet  in  thickness. 

FiG.  25. 


The  varieties  of  lamination  clearly  indicate  the  circumstances  under  which 
the  substance  of  a  rock  has  been  deposited  as  sediment,  or  the  conditions  to 
which  it  has  been  subjected  subsequent  to  its  deposition.  Thus,  parallel 
lamince  must  be  the  result  of  quiet  deposition  upon  a  level  surface.  Waved 
lamina,  in  many  instances,  are  manifestly  nothing  but  ripple  or  current  marks, 
such  as  may  be  seen  on  the  sands  of  the  sea-shore  when  left  dry  by  the  tide, 
and  at  the  bottom  of  any  clear  water  where  a  current  is  moving  over  a  sandy 
or  muddy  surface.*  Magnificent  examples  of  this  rippled  surface  may  be 
seen  upon  the  sandstones  and  shales  of  the  Connecticut  River  Valley.  Fig. 
26  illustrates  their  character.  Similar  undulating  ridges  and  farrows  may  be 
also  sometimes  seen  on  the  surface  of  drift  snow  and  blown  sand.  Oblique 
lamination  must  generally  have  been  the  result  of  deposition  upon  a  steep 
shore,  where  the  materials  were  driven  over  the  edge  of  an  inclined  plane. 

Highly  contorted  lamination  must  have  resulted  from  lateral  and  vertical 


QUESTION What  is  said  of  the  rippled  surfaces  of  rocks? 


*  "  Either  wind  or  -water,  as  they  roll  before  them  the  little  grains  of  sand,  tend  to  pile 
them  into  small  ridges,  which  are  perpetually  advancing  one  on  the  other,  in  consequence 
of  the  little,  grains  of  sand  being  successively  pushed  up  the  windward  or  weather  side  of 
the  ridge,  and  then  rolling  over  and  resting  on  the  lee  or  sheltered  side.  It  is  produced 
on  the  sea-beach,  not  in  consequence  of  the  ripple  of  the  wave  impressing  its  own  form  on 
the  sand  below,  which  wo'uld  be  an  impossibility,  but  because  the  moving  current  of 
water,  as  the  tide  advances  or  recedes,  produces  on  the  surface  of  the  sand  below  the 
same  form  as  the  moving  current  of  air  produces  on  the  surface  of  the  water  above.  A 
rippled  surface,  therefore,  to  a  rock  is  no  proof  of  its  having  been  necessarily  formed  in 
shallow  water,  though  rippled  surfaces  are  perhaps  more  frequently  formed  there,  but 
simply  a  proof  of  a  current  in  the  water  sufficient  to  move  the  sand  gently  along  at  what- 
ever depth  that  bottom  may  be  from  the  surface  of  the  water."—  Encyclopedia,  Bri~ 
tannica,  1S59. 


72         FIRST     PRINCIPLES     OF     GEOLOGY. 

FIG.  26. 


pressure.     Thus,  in  the  case  represented  by  Fig.  25,  it  is  clear  that  the  laminae 
could  not  have  been  deposited  originally  in  the  curved  position  represented  ; 


FiG. 


and,  therefore,  the  flexures  must  have  been  the  result  of  some  subsequent 
action.     It  would  also  appear  that  the  successive  laminae,  at  some  period  after 

QUESTION*.— What  must  have  been  the  cause  of  contorted  lamination  ? 


STRUCTURE    AND    RELATION    OF    ROCKS.       73 

their  deposition,  must  have  been  in  a  state  so  plastic  as  to  admit  of  bending 
without  breaking. 

Fig.  27  represents  an  example  of  contortions  in  a  bowlder  of  gneiss  and 
hornblende  schist  in  the  cabinet  of  Amherst  College. 

89.  Comparative  time  required  for  the  Formation  of 
Strata  and  Laminjc . — The  thickness  and  cdmposition  of  successive 
larnince  and  strata  enable  us  to  form  some  idea  of  the  comparative  time  re- 
quired for  their  formation.  Thus,  if  a  series  of  beds  have  precisely  the  same 
character  and  composition,  and  if  the  planes  of  lamination  and  of  stratifica- 
tion blend  into  one  another,  it  is  reasonable  to  suppose  that  the  intervals 
of  time  between  the  successive  depositions  were  comparatively  short,  and 
that  the  conditions  of  deposition  remained  unaltered  during  the  formation 
of  the  series  in  question.  If,  on  the  contrary,  the  successive  beds  present 
entirely  different  characters — if  a  bed  of  shale  is  succeeded  by  one  of  sand- 
stone, or  sandstone  by  limestone — a  much  longer  interval  between  the  suc- 
cessive depositions  may  be  properly  inferred,  since  some  time  must  have  been 
required  for  changes  to  take  place  in  the  conditions  of  the  neighborhood,  suf- 
ficient to  affect  the  character  of  the  depositions. 

When  strata  and  laminae  enclose  the  remains  of  fossil  animals  or  plants  it 
may  be  possible  to  obtain,  moreover,  somo  conception  even  of  the  absolute 
time  required  for  the  formation  of  the  rock  in  question.  Thus,  for  example, 
if,  in  strata,  we  find  shells  (see  Fig.  28),  or  the  remains  of  plants  in  such  per- 

FIG.  28. 


fectacss  and  positions  as  to  indicate  beyond  a  doubt  that  the  organisms  of 
which  they  once  constituted  a  part  originated,  lived  to  maturity,  died,  and 
were  gradually  inclosed  in  sediment  in  the  very  same  localities  in  which  their 
remains  now  exist,  it  is  impossible  to  escape  from  the  conclusion  that  the 
time  requisite  for  the  formation  of  two  successive  strata  was  at  least  equal  to  • 
the  time  necessary  for  the  organisms  enveloped  to  attain  maturity,  and  tho 
duration  of  this  period  may  bo  inferred  by  observing  the  development  of  cor- 
responding living  species.* 


QUESTIONS. — How  may  we  form  an  estimate!  of  the  time  required  for  the  formation  of 
strata  and  laminae  ?    What  inference  may  we  draw  from  fossils  in  undisturbed  positions  ? 


*  "  There  are  cases  in  which  we  find  on  the  surface  of  a  bed  of  limestone  the  roots  or 
attachments  of  a  particular  class  of  marine  fimmals,  called  cncrinites  (see  Fig.  29),  which, 
when  alive,  were  fixed  to  the  rock  by  a  solid  calcareous  base.  These  attachments  be- 
long to  animals  of  all  ages,  and  arc  in  great  numbers  ;  and  iu  a  bed  of  clay  or  shale  which 

4 


74 


FIRST     PRINCIPLES     OF     GEOLOGY. 


FIG.  29. 


90.  Position  of  the  Stratified  Rocks. 
— If  we  assume  that  the  materials  of 
which  the  stratified  rocks  are  composed 
were  originally  deposited  as  sediment  at 
the  botton  of  seas,  lakes,  etc.,  the  original 
position  of  strata  must  have  necessarily 
been  more  or  less  nearly  horizontal,*  and 
in  this  condition  we  sometimes  find  them. 
In  most  cases,  however,  the  beds  and  layers 
of  the  sedimentary  rocks  have  been  thrown, 
by  the  action  of  various  disturbing  forces, 
into  inclined  and  irregular  positions,  and 
sometimes  even  on  edge  ;  thus  producing 
extensive  surface  elevations  and  depres- 
sions. 

Fig.  30  represents  strata  in  different  positions ;  A, 
horizontal ;  B,  inclined ;  C,  highly  inclined,  or  on 
edge;  D,  thrown,  or  tilted  up.  Similar  appearances 


QUESTIONS. — "What  must  have  been  the  natural  position  of 
the  stratified  rocks  ?  In  what  position  are  they  usually  found  ? 


rests  immediately  on  the  limestones,  there  are  found  a  multi- 
tude of  the  remains  of  the  upper  portions  of  these  animals, 
likewise  of  all  sizes  and  ages.  Now,  it  is  plain  that  in  this  case, 
after  the  limestone  was  formed,  there  was  an  interval  during 
which  the  sea  was  quite  clear  and  free  from  sediment,  and, 
therefore,  well  adapted  for  the  growth  of  these  animals ;  and 
that  they,  after  a  time,  settled,  accordingly,  on  the  limestone  at 
the  bottom  of  the  sea,  and  grew  and  flourished  there  for  a  suf- 
ficient period  to  allow  of  successive  generations  arriving  at 
maturity  undisturbed  before  the  time  when  a  quantity  of  mud, 
having  been  carried  into  the  water,  was  deposited  upon  them, 
and  killed  them,  and  at  the  same  time  buried  their  remains. 
Hei'e,  then,  we  have  an  interval  of  many  years,  if  not  of  cen- 
turies, between  the  formation  of  two  beds  of  clay  and  limestone, 
which  rest  directly  one  upon  the  other/'—  Buckland"s  Bridge- 
water  Treatise  and  Jukes'  Manual  of  Geology. 

*  The  exceptions  to  the  general  rule— that  strata  were  origin- 
ally  deposited  in  a  more  or  less  horizontal  position — cannot  ex- 
tend very  widely,  or  affect  any  very  important  rocks.  Deposits 
now  taking  place  have  rarely  an  inclination  greater  than  10° 
over  any  considerable  extent  of  surface,  although  under  very 

favorable  circumstances,  as  when  sediment  accumulates  rapidly  on  steeply  shelving  coast- 
lines, strata  may  be  formed  with  an  inclination  of  from  15°  to  30°. 


STRUCTURE    AND    RELATION    OF    ROCKS.      75 


FIG.  30. 


may  be  seen  to  advantage  in  almost  all  railway  rock-cuttings,  in  ravines  ex- 
cavated by  water,  in  sea-cliffs  and  in  quarries. 

Evidence  in  favor  of  the  original  horizontal  deposition  of  inclined  strata 
may  sometimes  be  derived  from  the  arrangement  of  the  materials  that  enter 
into  their  composition.  Thus,  it  is  frequently  observed  that  vertical  or  highly 
inclined  strata  contain  pebbles  with  their  longer  axes  in  the  plane  of  the 
strata.  (See  Fig.  31.)  When  these  pebbles,  however,  were  deposited,  their 

FiG.  31. 


FIG.  32. 


longer  axes,  in  virtue  of  a  well-known  mechanical  principle,  would  naturally 
assume  a  horizontal  position  (i.  e.,  the  position  of  stable  equilibrium);  and, 
therefore,  their  present  position  must  have  resulted  from  a  change  in  the  posi- 
tion of  the  strata  in  which  they  are  in- 
closed. The  same  thing  may  be  also 
shown  by  the  position  of  fossils.  For 
example,  in  a  geological  formation  in 
the  south  of  England,  known  as  the 
"  Portland  Dirt  Bed,"  the  remains  of 
an  ancient  forest,  which  must  have 
grown  upon  a  comparatively  level  sur- 
face, are  found  imbedded  in  strata, 
inclined  at  a  high  angle.  (See  Fig. 
;  32.) 

91    flip, — The  angle  or  slope  at  which  a  stratum  inclines 
to  the  horizon  is  called  its  dip. 

Thus,  in  Fig.  31,  the  strata  are  represented  as  dipping  at  an  angle  of  nearly 
45°  with  the  plane  of  the  horizon. 

Dip  is  reckoned  from  0°  to  90°  ;  when  the  dip  is  90° 
the  strata  are  of  course  vertical. 


QUESTIONS.— What  evidence  do  we  find  that  inclined  strata  were  originally  horizonal? 
What  is  the  "  dip  "  of  strata  ?    How  is  it  reckoned  ? 


76 


FIRST      PRINCIPLE 


OF      GEOLOGY 


92.  Outcrop  and  Strike, — When  an  inclined  stratum 
comes  to  the  surface  (as  at  E;  Fig.  30),  its  exposed  edge 
is  called  its  outcrop;  and  the  direction  or  line  of  out- 
crop along  the  surface  of  the  ground  is  termed  its  strike. 

The  dip  and  strike  are  always  at  right  angles  to  each  other ;  so  that  if  a 
stratum  is  found  to  dip  either  to  tho  north  or  south,  we  may  be  sure  that  its 
strike  or  line  of  outcrop  has  an  east  and  west  direction. 

"  Dip  and  strike  may  be  aptly  illustrated  by  a  row  of  houses  running  east 
and  west ;  the  long  ridge  of  the  roof  representing  the  strike  of  the  stratum  of 
slates,  which  dip  on  one  side  to  the  north  and  on  the  other  to  the  south.  A. 
stratum  which  is  horizontal  or  level  in  all  directions  has  neither  dip  iior  strike." 
— LYELL. 

The  dip  of  a  stratum  is  sometimes  ascer- 
tained by  means  of  an  instrument  called  a 
a  clinometer,  but  for  most  purposes  it  can  be 
determined  with  sufficient  accuracy  by  the 
eye.  The  judgment  may  be  assisted  by  hold- 
ing tho  hands  before  the  eyes  in  the  position 
represented  in  Fig.  33,  and  observing  whether 
the  planes  of  the  inclined  strata  bisect  the 
right  angle  at  an  angle  of  45°,  or  whether 
the  inclination  be  greater  or  less  than  that 
amount. 

A  good  pocket  compass  will  answer  for 
finding  the  strike. 
FiG.  34. 


FIG.  33. 


Strata  sometimes  appear  horizontal,  when,  in  reality,  they  are  highly  in- 
clined. Thus,  the  strata  in  the  sea-cliff  (Fig  34),  to  an  observer  in  front, 

QUESTIONS. — What  is  understood  by  "outcrop"  and  "  strike?"  What  relation  do  the 
dip  and  strike  sustain  to  each  other?  llow  may  dip  and  strike  be  illustrated?  How 
may  dip  and  strike  be  ascertained  ? 


STRUCTURE  AND  RE  I,  AT  ION  OF  ROCKS.   77 

would  seem  to  be  horizontal,  while  a  person  on  the  side,  facing  a  section  at 
right  angles  to  the  strike  of  the  strata  would  at  once  perceive  that  they  have 
a  high  degree  of  inclination. 

93.  Anticlinah  and  Synclinals, — When  strata  dip  in 
opposite  directions  from  a  ridge  or  line  of  elevation,  like 
the  roof  of  a  house  (as  at  A,  Fig.  35),  the  ridge  is  said  to 
be  anticlinal  (Gr.  avri,  against,  and  K/Uvw,  I  bend),  and 
the  curve  formed  by  the  direction  of  the  strata  is  termed 
an  anticlinal  curve. 

On  the  other  hand,  when  strata  dip  toward  a  common 
line  of  depression  (as  at  B,  Fig.  35),  the  axis  or  line  is 
termed  synclinal  (aw,  together),  and  the  trough  or  valley, 
formed  by  such  a  dip,  is  called  a  synclinal  trough  or  valley. 

In  Fig.  35,  A  represents  anticlinal  and  B  synclinal  strata ;  the  beds  num- 
bered 6,  7,  8  being  repeated  on  each  side  of  both.  At  A  the  lower  beds,  1, 
2,  3,  4,  5  are  seen  rising  out  from  underneath  them  in  the  form  of  an  arch. 
At  B,tho  upner  beds,  9  to  13,  repose  upon  them  in  the  form  of  a  trough.  The 

FiG.  35. 


ft. 

Section  on  line  C  7) 

straight  line,  which  may  be  supposed  to  run  directly  from  the  eye  of  the 
spectator,  along  the  top  of  the  ridge  A,  or  the  bottom  of  the  trough  B,  is 
called  the  "axis"  of  the  curve  in  each  case. 

94.  Conformable  and  Unconformable  Strata, — When 
successive  strata,  or  groups  of  strata,  are  parallel  to  each 
other,  they  are  said  to  be  conformable  ;  when  not  parallel, 
they  are  unconformable. 

Thus,  in  Fig.  36,  the  upper  or  horizontal  series  rest  unconformably  on  the 
highly  inclined  series  beneath  them,  although  the  members  of  the  horizontal 
and  inclined  series,  considered  separately,  are  conformable.  The  inference  to 


QUESTIONS. — Wbat  are  anticlinals  and  synclinals  1    When  are  strata  said  to  be  con- 
formable, and  when  unconformable? 


78          FIRST     PRINCIPLES     OF     GEOLOGY. 

FiG.  36. 


to  be  deduced  from  a  natural  section  like  that  shown  in  Fig.  36,  is,  that  the 
lower  strata  were  formed  and  tilted  up  before  the  upper  and  unconformable 
strata  were  deposited  upon  them. 

FIG.  37. 


Fig.  3t  represents  a  striking  example  of  unconformable  strata,  figured  in 
the  geological  survey  of  Great  Britain,  as  occurring  in  South  Wales. 

FiG.  38. 


It  sometimes  happens  that  in  the  interval  between  the  deposition  of  two 
sets  of  beds,  the  inferior  rock  has  had  channels  or  hollows  cut  into  it  by  cur- 
rents of  water,  which  irregularities  have  been  subsequently  filled  up  by  a  part 
of  the  bed  next  deposited. 

QUESTION. — When  are  strata  said  to  be  conformable,  and  when  unconformable  ? 


STRUCTURE    AND    RELATION    OF    ROCKS.      79 


Fig.  38  represents  a  case  of  this  character,  figured  by  Mr.  Jukes,  from  the 
new  red  sandstone  formation  of  England. 

95.  Contortions .— Strata  which  have  been  subjected  to  the 
action  of  extensive  and  powerful  disturbing  forces,  rarely 
exhibit  a  uniform  dip  and  strike  over  any  considerable 
area,  but  are  often  bent  and  folded  upon  each  other,  or 
contorted  in  a  very  remarkable  manner.  These  bendings 
and  contortions  of  strata  occur  on  every  possible  scale, 
"from  mere  little  crumplings  on  the  side  of  a  bank,  to 
curves,  of  which  the  radii  are  miles,  and  the  nuclei  are 
mountain  chains." 

Some  curvatures  of  strata  are  remarkably  regular  and  symmetrical,  as  in 
Fig.  39,  which  represents  an  actual  section  of  strata  of  shales  and  limestones 
on  the  borders  of  Derbyshire,  England ;  in  other  cases,  especially  where  beds 
of  soft  material  alternate  with  hard  ones,  the  curvatures  are  exceedingly  ir- 
regular, as  is  represented  in  Fig.  23. 

FIG.  39. 


In  some  instances,  the  flexures  and  contortions  have  been 
sufficient  to  produce  actual  inversions  in  strata,  so  that 
beds,  which  were  originally  lowest  in  the  series,  are  made 
to  appear  uppermost,  and  as  of  recent  formation.  (See 
Fig.  40.) 

The  agencies  by  which  contortions  and  flexures  may  have  been  produced 
are  numerous.  Volcanic  forces  have;  undoubtedly,  in  many  instances  oper- 
ated from  beneath,  whereby  the  strata  have  been  bent  upward ;  on  the  other 
hand,  the  weight  of  superincumbent  material  would  contribute  to  bend  them 
downward ;  while  the  unequal  elevation  or  depression  of  portions  of  the  earth's 
crust  might  tend  to  subject  adjoining  strata  to  extreme  lateral  pressure. 


QUESTIONS.— What  is  said  of  the  contortions  of  strata?    Are  strata  ever  found  com- 
pletely inverted  ?    How  have  contortions  of  strata  probably  been  produced 


80          FIRST     PRINCIPLES     OF      GEOLOGY. 

FIG.  40. 


"  "We  may  illustrate  the  effects  which  lateral  pressure  may  produce  on 
flexible  strata,  by  placing  several  pieces  of  differently  colored  cloths  upon  a 
table,  and  when  they  are  spread  out  horizontally,  covering  them  with  a  book. 
Then  apply  other  books  to  each  end,  and  force  them  toward  each  other.  The 
folding  of  the  cloths  will  exactly  imitate  those  of  bent  strata"  (see  Fig.  41). — 
LYELL. 

FIG.  4L 


96.  Thickness  of  Strata. — The  displacements  and  curvatures  of 
strata  afford  a  ready  means  of  calculating  the  thickness  of  different  sedimentary 
deposits  and  also  of  determining  the  character  of  the  crust  of  the  globe  to  a  depth 

FJO.  42. 


far  beyond  the  skill  of  man  to  penetrate ;  since  by  measuring  across  the  up- 
turned edges  of  a  series  of  strata  (as  in  Fig.  42,  which  represents  actual  curva- 
tures of  strata  in  the  Alps  of  Switzerland),  we  ascertain  at  once  their  thick- 


QTTESTIONS.— How  may  the  effects  of  lateral  pressure  on  strata  be  illustrated?    How 
do  the  displacements  and  curvatures  of  strata  allow  us  to  calculate  their  thickness  ? 


STRUCTURE  AND  RELATION  OF  ROCKS.   81 

ness,  and  also  the  depth  to  which  they  must  have  originally  extended  into 
the  earth  when  occupying  a  horizontal  position.* 

By  measurements  and  calculations  of  this  character,  the  stratified  fossilifer- 
ous  rocks  of  Europe  have  been  estimated  to  be  at  least  ten  or  twelve  miles 
thick ;  while,  according  to  Prof.  H.  D.  Rogers,  the  maximum  thickness  of 
the  stratified  fossiliferous  rocks  of  the  United  States,  lying  below  the  upper- 
most beds  of  the  coal  series,  cannot  be  less  than  30,000  or  35,000  feet  (six  to 
seven  miles). 

97.  Joints, — In  addition  to  the  separation  of  rock- 
masses  into  beds  and  layers  by  planes  of  division,  which 
were  obviously  the  result  of  intervals  in  the  acts  of  deposi- 

FIG.  43. 


tion  of  sediment,  all  rocks — stratified  and  unstratified — 
are  traversed  by  other  divisional  planes  called  joints.  These 
"natural  fissures,"  traverse  the  rock  in  various  directions 


QUESTION.— What  estimate  has  been  made  of  the  thickness  of  the  fossiliferous  stratified 
rocks  ? 


*  "  Suppose  we  see  a  mountain  composed  of  a  particular  substance,  with  strata,  or 
other  beds  of  rock,  lying  against  its  sloped  sides,  we,  of  course,  infer  that  the  substance 
of  the  mountain  dips  away  under  the  strata  which  we  see  lying  against  it.  Suppose  that 
we  walk  away  from  the  mountain,  aci'oss  the  the  turned-up  edges  of  the  stratified  rocks, 
and  that  for  many  miles  we  continue  to  pass  over  other  stratified  rocks,  all  disposed  the 
same  way,  till,  by  and  by,  we  come  to  a  place  where  we  begin  to  cross  the  opposite  edges 
of  the  same  beds ;  after  which,  we  pass  over  these  rocks  all  in  a  reverse  order,  till  we 
come  to  another  mountain  composed  of  similar  materials  to  the  first,  and  shelving  away 
under  the  strata  in  the  same  way.  We  should  then  infer  that  the  stratified  rocks  occu- 
pied a  basin,  formed  by  the  rock  of  these  two  mountains,  and  by  calculating  the  thickness 
right  through  these  strata,  could  be  able  to  say  to  what  depth  the  rock  of  the  mountain 
extended  below." — Vestiges  of  the  Natural  History  of  Creation. 

4* 


82          FIRST     PRINCIPLES     OF     GEOLOGY. 

and  separate  it  into  blocks  of  various  shapes  and  sizes, 
regular  and  irregular. 

Fig.  43  represents  joints  in  limestone.  The  planes  of  stratification  are 
shown  by  the  parallel  lines  dipping  from  the  spectator  and  toward  the  left. 
The  other  lines  are  the  ends  of  joint  planes,  which  also  form  the  smooth  sur- 
faces of  the  rock,  nearly  at  right  angles  to  each  other,  as  shown  by  the  pro- 
jecting corners. — JUKES. 

u  "Without  natural  joints  the  quarrying  of  stratified  rocks  would  be  very 
difficult,  and  that  of  unstratified  rocks  almost  impossible.  If  beds  of  sand- 
stone or  limestone  were  undivided  by  natural  joints,  each  block  would  have 
to  be  cut  or  split  by  artificial  means,  on  every  side,  from  the  rest  of  the  bed ; 
but  in  rocks,  such  as  granite  and  greenstone,  which  have  no  beds,  the  blocks 
would  not  only  have  to  be  cut  on  each  side,  but  underneath  also.  It  would 
obviously  be  a  most  impracticable  task  to  dig  out  a  large  block  of  granite 
from  the  midst  of  a  solid  mass,  untraversed  by  any  natural  planes  of  division 
of  any  kind." — JUKES. 

Origin  of  Joints  , — It  is  exceedingly  difficult,  in  many  cases,  to  satis- 
factorily explain  the  origin  of  joints  in  rock -masses.  In  general,  they  are 
believed  to  be  the  result  of  a  shrinkage  or  contraction  of  the  rocks  consequent 
upon  consolidation.  In  some  instances,  however,  they  are  undoubtedly  the 
result  of  mechanical  upheaval  and  disturbance,  while  in  others,  the  lines  of 
fissure  have  definite  compass-bearings,  are  arranged  in  sets,  and  seem  to  obey 
some  general,  but  as  yet  undetermined  law.  That  they  have  been  formed 
since  the  original  accumulation  of  the  rock-material  is  evident  from  the  fact 
that  they  not  only  pass  through  strata  and  lamina?,  but  also  through  pebbles, 
fossils,  and  crystalline  aggregations  embedded  within  the  rock-material.  One 
of  the  most  striking  examples  of  this  action  occurs  in  a  conglomerate  rock, 
at  a  well-known  locality,  "Purgatory,"  near  Newport,  E.  I.,  where  pebbles 
of  various  sizes  and  of  the  hardest  material  are  as  smoothly  divided  in 
given  planes  as  if  a  succession  of  clean  cuts  had  been  made  crosswise,  with  a 
sharp  instrument,  through  the  entire  mass  of  the-  rock  in  which  they  are  em- 
bedded. 

98.  Faults,  or  Dislocations.— When  the  continuity  of 
strata  has  been  broken  in  consequence  of  an  upheaval,  it 
sometimes  happens  that  the  beds  on  opposite  sides  of  the 
fissure,  or  line  of  fracture,  are  left  at  very  different  levels 
— many  feet,  or  many  hundreds  of  feet  above  or  below 
the  parts  with  which  they  were  once  continuous.  Such 

QUESTIONS.—  Iu  what  manner  are  rocks  divided  by  joints?  How  do  joints  assist  the 
quarrying  of  rocks  ?  What  is  said  of  their  origin  ?  What  proof  is  there  that  joints  have 
been  formed  since  the  accumulation  of  the  rock-material  ?  What  are  faults  ? 


STRUCTURE    AND    RELATION    OF    ROCKS.       83 

a  displacement  is  termed  a  "fault"    or    "dislocation." 
(See  Fig's  44,  and  158.) 

The  interruptions  occasioned  by  faults  are  a  source  of  considerable  difficulty 
in  mines — especially  in  coal  mines — since,  when  a  fault  is  reached,  it  is  almost 
impossible  to  decide  whether  the  continuation  of  the  mineral  sought  is  above 
or  below  the  level,  or  to  the  right  or  the  left.  In  the  great  Newcastle 

FiG.  44. 


coal  district  of  England,  the  upward  or  downward  movement  of  strata  has 
amounted  to  nearly  1,000  feet,  so  that  the  surface  of  the  ground  must  have 
been  originally  affected  to  that  extent — portions  having  either  risen  or  sunk 
1,000  feet  above  or  below  the  rest.  These  projections  or  inequalities  have 
been  subsequently  removed  by  denudation,  and  their  former  existence  can 
now  only  be  discovered  by  studying  the  internal  structure  of  the  underlying 
strata. 

In  some  instances,  the  "  fault  -fissures"  are  mere  planes  of  division,  and 
not  unfrequently  the  contiguous  surfaces  of  the  fault  are  found  to  be  quite 
smooth  and  polished  by  the  enormous  friction  that  has  taken  place — an  ap- 
pearance termed  by  geologists  "  slicken-side"  In  other  cases  the  fault-fissures 
are  open,  but  most  of  the  originally  open  fissures  have  been  filled  with  angular, 
dispersed  fragments  from  the  adjoining  rocks,  or  have  become  the  repositories 
of  minerals  that  have  been  subsequently  introduced  into  them.  These  min- 
erals are  usually  in  a  crystalline  form,  and  commonly  consist  of  quartz,  cal- 
careous spar,  fluor  spar,  heavy  spar  (sulphate  of  barytes),  together  with  ores 
of  lead,  copper,  zinc,  tin,  iron,  etc. 

Fig.  45  represents  a  vein  of  lead  (galena)  embedded  in  calc  spar,  which 
fills  a,  fissure  in  gneiss,  at  Rossie,  St.  Lawrence  County,  N.  Y. — Emmons' 
American  Geology,  p.  133,  Part  I. 


QUESTIONS.— How  do  faults  occasion  interruption  in  mining  enterprises?    How  have 
many  mineral  veins  originated  ? 


84 


FIRST     PRINCIPLES     OF     GEOLOGY. 


FIG.  45.  Fissures  containing  ores  of  the 

metals  are  termed  "mineral  veins," 
or  "lodes." 

Many  valleys,  gorges,  and  ra- 
vines, were  probably,  in  the  first 
instance,  merely  fissures,  or  lines 
of  fracture,  which  have  subse- 
quently been  widened  by  the 
action  of  water  and  partially  filled 
up  with  loose  material.  In  like 
manner,  a  fracture  in  the  rock 
which  does  not  extend  to  the 
surface,  may,  in  time,  by  serving 
as  a  channel  for  water,  become  a 
cavern;  and  such,  doubtless,  has 
been  the  origin  of  many  of  the 
extensive  caverns  existing  in 
limestone. 

I  99.  Cleavage.  —  Some 
stratified  rocks  have  a  sus- 
ceptibility to  split  into 
straight,  parallel  plates, 
which  maintain  a  certain 
given  direction  over  wide 
areas,  and  are  independ- 
ent of,  and  often  not  co- 
incident with  the  planes 
of  either  stratification  or 
lamination.  Such  a  struc- 
ture is  called  cleavage. 

Cleavage  structure  is  most  com- 
mon and  most  perfect  in  clay  or 
argillaceous  slate  (common  slate), 
though  it  is  sometimes  apparent 
in  limestone  and  sandstones,  and 
is  always  most  perfect  in  tho  finest 
grained  rocks. 

Cleavage  planes  are  often  inclined  30®  or  40°  to  the  planes  of  stratification 
and  lamination,  arid  not  unfrequently  the  two  sets  of  planes  are  at  right  angles 


QUESTIONS.— What  has  been  the  origin  of  some  valleys,  ravines,  and  caverns?    What 
Is  cleavage  ?    In  what  rocks  is  cleavage  most  perfect  ? 


STRUCTURE    AND    RELATION    OF    ROCKS.      85 

to  each  other.  In  other  instances,  as  may  bo  often  noticed  in  the  finer  slates 
of  this  country,  the  cleavage  coincides  with  the  original  bedding  or  lamina- 
tion. 

Cleavage  planes  are  remarkable  for  their  almost  perfect  parallelism,  no 
matter  how  much  the  strata  and  their  lamina?  may  be  disturbed  and  con- 
torted. Fig.  46  represents  a  set  of  cleavage  planes  (figured  by  Prof.  Sedg- 
wick)  crossing  highly  curved  strata  of  slate  in  Wales. 

FIG.  46. 


Origin  of  Cleavage . — Geologists  are  not  fully  agreed  as  to  the 
origin  of  cleavage.  Some  regard  it  as  a  kind  of  crystallization,  induced  in 
the  particles  of  the  rock  by  the  action  of  heat  or -electro-chemical  forces.  This 
theory,  which  has  been  called  the  chemical,  derives  strong  support  from  the 
fact  that  a  kind  of  artificial  cleavage  can  be  produced  by  subjecting  masses  of 
moistened  clay  to  the  long-continued  action  of  weak  galvanic  currents. 

Another  theory  refers  the  origin  of  cleavage  to  a  mechanical  compression 
of  the  strata  applied  at  right  angles  to  the  cleavage  planes;  and,  in  support  of 
this  view,  Prof.  Tyndall,  of  England,  has  experimentally  shown  that  fine  clay, 
or  almost  any  impalpable  material,  as  white-lead,  wax,  or  even  cheese,  when 
subjected  to  pressure,  and  at  the  same  time  allowed  to  spread  laterally,  may 
become  endowed  with  the  property  of  cleaving,  or  splitting  in  lines,  perpen- 
dicular to  the  direction  of  the  pressure.  Another  fact,  considered  as  con- 
firmatory of  the  mechanical  theory  of  cleavage,  is,  that  fossils  and  other  small 
bodies  embedded  in  rocks  possessing  a  cleavage  structure,  are  not  unfre- 
quently  distorted ;  being  lengthened  and  pulled  out,  as  it  were,  in  the  direc- 
tion of  the  cleavage,  and  contracted  in  an  opposite  direction. 

100.  Foliation, — This  name  has  been  applied  to  a 
structure  superinduced  in  some  rocks  subsequent  to  their 
original  deposition,  which  imparts  to  them  a  tendency  to 
split  into  plates  or  layers  of  different  mineral  composition, 
either  coincident  with  the  bedding  or  across  it.  Cleavage, 
on  the  contrary,  implies  only  a  tendency  to  split  in  a  mass 
of  the  same  composition. 

The  rocks  in  which  a  foliated  structure,  according  to  the  above  definition, 
is  most  apparent,  are  mica  schist  and  gneiss — the  former  often  separating  into 

QUESTIONS. — What  is  said  of  the  parallelism  of  the  planes  of  cleavage  ?  What  is  the 
supposed  origin  of  cleavage  ?  What  is  foliation  ?  What  rocks  especiall7  exhibit  foliation  1 


86         FIRST     PRINCIPLE'S     OF     GEOLOGY. 

distinct  plates  or  layers  of  mica  and  quartz,  and  the  latter  into  layers  of  mica, 
quartz,  and  feldspar. 

101.  Concretionary  Structures,— Rocks  are  often  per- 
vaded by  concretionary  structures  or  masses,  which  differ 
to  a  greater  or  less  extent  in  composition  from  the  sub- 
stance of  the  inclosing  rock,  and  are  usually  of  a  spherical 
or  cylindrical  form.  These  structures  appear  to  owe  their 
origin,  in  general,  to  a  tendency  which  any  mineral,  dif- 
fused in  a  state  of  minute  subdivision  through  a  mass  of 
different  nature,  seems  to  have,  to  segregate  itself  from  the 
mass,  and  collect  about  certain  centers. 

Clayston  es . — A  well-known  variety  of  these  concretions  occur  in  beds 
of  clay,  containing  disseminated  carbonate  of  lime,  and  are  familiarly  known 
by  the  name  of  "  clay  stones."  They  assume  almost  every  variety  of  form; 
some  being  as  smooth  and  symmetrical  as  if  turned  on  a  lathe,  while  others 
have  not  unfrequently  a  mimic  resemblance  to  animals  or  artificial  products. 
Fig.  47  represents  some  of  the  most  common  forms  of  these  bodies. 

FIG.  47. 


According  to  popular  credence  claystones  are  the  work  of  water,  and  are 
sometimes  even  regarded  as  artificial ;  but  the  -true  cause  of  their  formation 
is,  undoubtedly,  the  segregation  and  crystallizing  influence  of  carbonate  of 
lime.  This  mineral,  originally  disseminated  through  the  mass  of  the  clay  in 
small  quantities,  tends  to  collect  around  some  point,  as  a  nucleus — as,  for  ex- 
ample, an  organic  body — and  assume  a  crystalline  form.  The  presence  and 
contact  of  the  inert,  non-crystallizing  particles  of  finely  divided  clay,  how- 
ever, obstructs,  and  in  part  prevents,  this  crystallizing  tendency,  and  the  re- 
sult is  an  imperfect  or  semi-orystallization,  producing  globular  or  curve-sur- 
faced solids,  composed  of  a  mixture  of  clay  and  carbonate  of  lime.  Similar 
phenomena  are  often  observed  in  laboratory  processes,  where  the  presence  of 


QUESTIONS. — What  is  said  of  the  concretionary  structure  of  rocks?    What  are  clay- 
stones?    What  is  the  supposed  origin  of  claystones  ? 


STRUCTURE    AND     RELATION    OF    ROCKS        87 


finely  divided  and  diffused  particles  of  foreign  substances  partially  arrests  the 
formation  of  crystals.* 

In  addition  to  the  claystones  described,  a  great  variety  of  other  concretion- 
ary structures  are  recognized.  Iron  pyrites  (bi-sulphate  of  iron),  and  other 
ores  of  iron,  are  very  frequently  found  yIG>  43. 

disseminated  in  rocks  in  the  form  of 
rounded  or  nodular  masses.  The  vari- 
ety of  iron  ore  known  as  <:  hematite" 
furnishes  beautiful  specimens  of  con- 
cretions, which  have  a"  minutely  radi- 
ated structure  at  right  angles  to  the 
mass.  (See  Fig.  48.) 

Examples  of  concretionary  structure 
abound  also  in  limestones,  especially  in 
the  magnesian  limestone ;  the  spherical 
masses  varying  in  size  from  a  mere  glob- 
ule to  many  feet  in  diameter.  Fig.  49  represents  the  manner  in  which  nodules 
of  nearly  pure  silica  (flint)  are  frequently  distributed  in  beds  of  white  chalk ; 
and,  before  the  introduction  of  the  percussion-cap,  such  nodules,  from  the 
chalk  beds  of  England  and  France,  furnished  the  material  for  the  manufac- 
ture of  gun-flints. 

FiG.  49. 


S  e  p  t  a  r  i  a  . — Some  nodules  or  concretions,  when  broken  open,  are  often 
found  to  be  traversed  by  cracks  in  all  directions,  more  or  less  filled  up  with 

QUESTION. — "What  are  other  common  forms  of  concretions  ? 


•  Most  mineral  substances  refuse  to  crystallize  in  the  presence  of  a  large  amount  cf  im- 
purities, but  the  force  exerted  by  carbonate  of  lime  in  crystallizing  is  so  energetic  that  it 
can  form  regular  rhomboids,  even  when  incorporated  with  fifty  per  cent,  of  its  -weight  of 
sand.  If  the  impurity  exceeds  this  percentage  the  action  of  the  crystallizing  force  will 
tend  to  produce  spheroidal  forms. 


88 


FIRST      PKINCIPLES     OF     GEOLOGY. 


FIG.  50.  crystalline  spar.     (See  Fig.  50.)     Such  nodules  are 

termed  septaria  (Lat.  Septum,  a  division),  and,  when 
cut  and  polished,  frequently  present  a  highly  orna- 
mental appearance.  Some  varieties  of  septaria — 
those  composed  of  argillaceous  limestone — furnish, 
when  ground  and  pulverized,  the  finest  hydraulic 
mortar,  or  "  Roman  cement."* 

102.  Structure  of  the  Igneous  Rocks, — One  of  the  prin- 
cipal characteristics  of  the  igneous  rocks  k  a  want  of  strati- 
fication— that  is  to  say,  their  constituent  ingredients  do 
not  exhibit  any  marks  of  arrangement  such  as  might  arise 
from  suspension  or  drifting,  nor  any  such  proofs  of  me- 
chanical action  as  worn  and  rounded  pebbles  or  grains  of 
sand.  On  the  contrary,  the  igneous  rocks  are  mostly  crys- 
talline rocks. 

The  granites,  syenites,  and  porphyries  have  always  a  more  or  less  jointed 
structure,  which  is  sometimes  sufficiently  regular  to  impart  an  appearance  of 
stratification.  In  general,  however,  the  divisional  joints  of  tho  granitoid 

FIG.  51. 


rocks  are  extremely  irregular,  and  weathered  vertical  sections  of  these  rocks, 
consequently,  often  seem  composed  of  huge  blocks,  artificially  fitted  upon 
each  other.  Fig.  51  represents  a  jointed  structure  in  granite. 

QUESTIONS.— What  are  septaria  ?  What  is  the  principal  characteristic  of  the  igneous 
rocks? 

*  Most  limestones  which  contain  about  twenty  per  cent,  of  clay  (silicate  of  alumina) 
afford  a  lime  which  possesses  the  property,  wheu.  made  into  mortar,  of  hardening  under. 
Such  mortara  are  termed  hydraulic. 


FIG.  52. 


STBUCTUKE    AND    RELATION    OF   BOCKS.      89 

103.  Prismatic  Structure  . — Certain  igneous  rocks,  especially  those 
which  occur  in  thin  sheets  or  wall-like  masses  overlying  or  traversing  other 
rocks>  are  divided  by  a  series  of  joints  into  a  multitude  of  prismatic  or  col- 
umnar blocks,  more  or  less  regular.  This  structure  is  remarkably  displayed 
in  certain  rocks  belonging  to  the  trap-group — basalt  and  greenstone — but  it 
may  also  be  occasionally  observed  in  lavas,  and  sometimes  even  in  granite 
or  aqueous  rocks,  which  are  in  close  proximity  to  masses  of  igneous  rocks. 
The  sides  of  these  prisms  are  sometimes  regu- 
lar and  equal,  producing  hexagonal,  pentagonal, 
or  other  forms ;  or  they  may  be  unequal  and 
irregular,  and  give  rise  to  uneven  and  wrinkled 
prisms. 

In  columnar  or  prismatic  basalt  and  green- 
stone, the  prisms  are  often  separated  at  inter- 
vals by  other  joints  into  short  blocks  (see  Fig. 
52),  whose  extremities  are  sometimes  flat  and 
sometimes  curved  into  convex  and  concave  surfaces,  which  fit  into  each  other 
somewhat  after  the  manner  of  a  ball  and  socket  joint.  In  other  cases,  the 
columns  are  simply  continuous  from  the  top  to  the  bottom  of  the  mass. 

In  length  and  diameter  the  columns  vary  exceedingly :  McCulloch  mentions 
some  at  the  Isle  of  Sky,  which  are  about  400  feet  long ;  others  have  been 
noted  as  not  exceeding  an  inch  in  length.  In  diameter,  they  range  from  nine 
feet  to  less  than  an  inch ;  but  the  most  regular  and  symmetrical  pillars  of 
basalt  are  usually  from  six  to  eighteen  inches  in  diameter.  In  greenstone 
the  prismatic  structure  is  commonly  on  a  larger  scale  than  in  basalt,  and  is 
generally  more  imperfect,  and  in  some  instances  the  columnar  structure  is 
most  noticeable  when  the  rock  is  viewed  at  a  distance,  as  at  the  Palisades  on 

FIG.  53. 


the  Hudson.  Usually  the  columns  stand  perpendicularly,  and  so  closely  com- 
pacted that,  though  perfectly  separable,  there  is  no  perceptible  space  between 
them.  (See  Fig.  52.)  Sometimes,  however,  they  are  curved  (see  Fig.  53), 


QUESTIONS. — What  rocks  have  a  prismatic  or  columnar  structure?    Describe  the  col- 
umnar forms  of  basalt  and  greenstone  ? 


90 


FIRST     PRINCIPLES      OF     GEOLOGY. 


or  even  horizontal.     Fig.  54  represents  a  basaltic  vein  divided  into  horizontal 
prisms,  on  the  northwest  shore  of  Lake  Superior. 

FIG.  54. 


The  columnar  structure  of  basalt  and  greenstone  has  produced  some  of  the 
most  remarkable  natural  scenery  on  the  globe.  In  Europe,  the  "  Giants 
Causeway,"  in  the  north  of  Ireland,  and  "Fingal's  Cave,"  at  the  Isle  of  Staflfa 
(one  of  the  western  islands  of  Scotland),  are  well-known  examples.  The 

FIG.  55. 


STRUCTURE    AND    RELATION    OF    ROCKS.       91 

former  consists  of  an  irregular  group  of  hundreds  of  thousands  of  pentagonal, 
jointed  basaltic  columns,  varying  from  one  to  five  feet  in  thickness,  and  from 
twenty  to  two  hundred  feet  in  height ;  the  whole  extending  out  into  the  sea 

FIG.  56. 


like  an  artificial  causeway  or  landing.    Fingal's  Cave  (seo  Fig.  55)  is  a  natural 
cavern  of  great  beauty,  which  has  been  produced  by  the  degradation  and  re- 
Fin.  57. 


92  FIRST     PRINCIPLES     OF     GEOLOGY. 

moval  of  basaltic  columns  by  the  action  of  the  waves.  The  perpendicular 
pillars  which  inclose  it  are  overlaid  by  a  mass  of  the  same  rock,  which  is 
entirely  wanting  in  prismatic  arrangement. 

Remarkable  examples  of  the  same  structure  occur  also  among  the  basalts 
and  greenstones  of  our  own  country,  especially  in  the  region  bordering  on  the 
northwest  coast  of  Lake  Superior.  Fig.  56  represents  a  mass  of  basaltic 
columns  resting  on  sedimentary  strata  from  this  locality,  figured  by  Dr.  Owen, 
U.  S.  Geologist.  Greenstone  columns  (less  regular  than  basalt),  standing  up- 
right, or  leaning  only  a  few  degrees,  are  also  quite  common  in  the  United 
States,  and  constitute  some  of  our  most  interesting  scenery.  Of  these,  the 
Palisades  on  the  Hudson  are  a  well-known  example.  They  also  occur  on 
the  Penobscot  river,  in  Maine,  and  very  perfectly  on  Mounts  Holyoko  and 
Tom,  on  the  Connecticut  river,  in  Massachusetts. 

Fig.  57  represents  an  overhanging  group  of  greenstone  columns,  at  Mount 
Holyoke,  figured  by  Professor  Hitchcock.  The  lower  ends  of  the  columns 
have  exfoliated  in  such  a  manner  as  to  present  a  convex  surface  downward. 

104.  Origin  of  Prismatic  Structure. — The  prismatic  or  col- 
umnar structure,  observable  in  trap  and  other  rocks,  has  been  shown,  by 
experiment,  to  be  due  to  the  manner  in  which,  the  rock  cooled  and  consoli- 
dated from  a  state  of  fusion.  Mr.  Gregory  Watt,  of  England,  melted  seven 
hundred  weight  of  basalt  in  a  blast  furnace,  and  kept  it  in  the  furnace  for  a 
number  of  days  after  the  fire  was  reduced.  He  found  that  it  fused  into  a 
dark-colored,  vitreous  mass,  with  less  heat  than  was  necessary  to  melt  pig- 
iron,  and  when  cooled  rapidly  and  in  small  quantities  yielded  a  slag-like 

FIG.  58. 


glass,  not  differing  in  appearance  from  obsidian.     When  refrigeration,  how- 
ever, took  place  slowly,  and  considerable  quantities  of  the  molten  material 

QUESTIONS. — What  are  some  remarkable  examples  of  columnar  basalt  and  greenstone  ? 
What  is  the  supposed  origin  of  the  columnar  structure  in  rocks  ?  Describe  Mr.  Watt's 
experiment? 


POSITION     OF      THE     IGNEOUS     ROCKS.         93 

were  concerned,  the  following  results  were  noted :  the  mass  returned  to  its 
original  stony  condition,  and,  during  the  process,  small  globules  made  their 
appearance,  which  gradually  increased  in  size  by  the  successive  formation  of 
external  concentric  coats,  like  those  of  an  onion,  so  that,  ultimately,  a  num- 
ber of  solid  balls  were  formed,  which  continued  to  enlarge,  until  they  pressed 
laterally  against  each  other,  and  became  converted  into  short,  polygonal 
prisms.  (See  Fig.  58.)  It  was  also  evident  that  if  many  layers  of  these  sphe- 
roids could  have  been  formed  in  a  mass  of  cooling  basalt,  one  above  the  other,  a 
long  column  of  separate  prisms  would  have  resulted  (as  in  Fig.  54)  with  the 
top  and  bottom  of  each  joint  flat,  concave,  or  convex,  according  to  variations 
in  the  amount  and  direction  of  the  pressure  at  the  ends  of  the  columns.  It 
has  also  been  observed  that  the  direction  of  the  prisms  or  columns  of  basalt 
and  greenstone  is  usually  at  right  angles  to  the  greatest  extension  of  the 
mass,  being  vertical  in  a  horizontal  vein  or  bed,  and  horizontal  in  a  vertical 
one,  thus  showing  that  the  divisional  structure  commenced  at  the  greatest 
cooling  surface,  and  thence  struck  in  toward  the  center  of  the  mass. 

105.  Position  of  the  Igneous  Rocks  and  their  relation 
to  t h e  * S t r a t i f i e d  Rocks ,— The  igneous  (uristratified)  rocks 
are  found  in  the  crust  of  the  earth,  under  the  following 
conditions  :  1.  As  irregular  masses  underlying  the  stratified 
rocks  (a,  a,  Fig.  59).  2.  As  veins  crossing  and  divid- 
ing rocks  of  every  description  (6,  &).  3.  As  irregular 
masses,  disrupting  (e),  overlying  (d),  or  intervening  be- 
tween strata  (c). 

FiG.  59. 

a 


>  a       !b        ~b          a  d        c  e 

Granite  generally  makes  its  appearance  at  the  surface  in  large  irregular 
masses  (as  at  a  and  e,  Fig.  59),  occupying  considerable  areas,  and  extending 
beneath  the  stratified  rocks  to  an  unknown  depth  in  the  interior  of  the  earth. 
Veins  of  granite,  often  branching  and  crossing  each  other,  sometimes  proceed 
from  these  masses,  and  penetrate  the  adjoining  rocks.  These  veins  are,  in 
some  instances,  miles  in  length. 

Fig.  60  represents  granite  underlying  and  penetrating  mica  schists  from  a 


QUESTIONS. — Under  what  conditions  are  the  igneous  rocks  found  in  the  crust  of  the 
earth  ?    What  is  the  general  position  of  granite  ? 


94 


FIRST     PRINCIPLES     OF     GEOLOGY. 


section  in  Cornwall,  England:  a,  a,  granite  veins;  I,  b,  mica  schist;  c,  un- 
derlying mass  of  granite.     Fig.  61  shows  two  exceedingly  tortuous  and  small 

FIG.  60. 

ft 


veins  of  granite  (figured  by  Dr.  Hitchcock),  in  limestone,  at  Colrain,  Massa- 
chusetts. 

The  trappean  and  volcanic  rocks  do  not,  in  general,  possess  the  massive 
FIG.  61. 


structure  of  granite  or  occupy  so  continuous  areas  of  the  earth's  surface.* 
They  may  be  especially  characterized  as  intrusive  and  overlying  rocks.f 


QUESTION.— What  are  the  characteristics  of  the  trappean  and  volcanic  rocks ? 


*  The  largest  area  occupied  by  trap-rocks  appears  to  be  in  India,  where  they  are  re- 
ported to  cover  an  area  of  200,000  square  miles.  In  Europe,  one  of  the  most  extensive 
developments  of  trap  (basalt)  occurs  in  the  north  of  Ireland,  and  covers  an  area  of  coun- 
try fifty  miles  long  by  thirty  wide,  to  a  depth  of  300  or  400  feet.  This  locality  includes 
the  celebrated  "  Giant's  Causeway."  (See  §  40.) 

t  According  to  Humboldt  (Cosmos,  vol.  I.),  "  there  is  a  special  difference  in  the  eruptive 
manifestations  of  the  granitic  rocks  as  contrasted  with  the  trappean  and  volcanic.  Thus, 
the  latter  appear  as  band-like  streams,  but  by  the  confluence  of  several  of  them  may 
cover  an  extensive  area.  Wherever  it  has  been  possible  to  trace  basaltic  eruptions  they 
have  generally  been  found  to  terminate  in  slender  threads.1'  Granatoid  rocks,  on  the 
contrary,  "with  the  exception  of  occasional  veins,  were  probably  not  eruptive  in  a  state 
of  fusion,  but  merely  in  a  softened  condition — not  from  narrow  fissures,  but  from  long 
and  widely  extended  gorges.  They  have  been  protruded,  but  have  not  flowed  forth,  and 
are  found  not  in  streams,  but  in  extended  masses." 


VEINS     AND     DIKES. 


95 


106.  Veins, — Veins  of  igneous  rock  are  usually  the  re- 
sult of  the  injection  of  liquid  (molten  ?)  rock-matter  into 
fissures,  which  either  previously  existed,  or  were  formed 
at  the  time  of  the  injection.  Such  veins  are  known  as 
veins  of  injection,  and  can  often  be  traced  to  a  large  mass 
of  similar  rock,  from  which,  as  they  proceed,  they  gener- 
ally subdivide  and  diminish  to  mere  threads. 

Fig.  62  represents  an  injection  vein  of  porphyry  traversing  argillaceous 
slate,  ou  the  coast  of  Cornwall,  England. 

FlG.  62. 


107.  Dike, — This  term  is  applied  by  geologists  to  wall- 
like  masses  of  igneous  rocks  (generally  trap,  porphyry,  or 
lava)  which  traverse  other  rocks,  and  appear  to  have  been 
produced  by  the  intrusion  of  melted  rock-matter  into  rents 
and  fissures. 

Dikes  arc  distinguished  from  veins  by  thoir  greater  magnitude,  by  the 
parallelism  of  their  sides,  by  their  not  ramifying  into  smaller  veins,  and  by 
the  greater  uniformity  of  their  contents.  When  the  matter  of  the  dike  is 
harder  than  the  intersected  strata,  and  the  latter  have  been  subjected  to  wear 
and  degradation,  the  igneous  mass  frequently  projects  abovu  the  surface  like 
a  wall,  and  may  be  traced  for  miles  across  a  country ;  hence  the  name  from 
the  Scotch  "dike"  a  wall  or  fence. 

QUESTIONS.—  What  is  the  assumed  origin  of  veins  of  igneous  rocks  ?  What  is  a  dike  ? 
How  are  dikes  distinguished  from  veins  ? 


96 


FIRST     PRINCIPLES     OF     GEOLOGY. 


Fig.  63  represents  a  characteristic  appearance  of  a  trap-dike  a,  entirely  in- 
terrupting the  continuity  of  the  strata  of  the  rock  c;  and  &,  a  dyke  which 
does  not  rise  to  the  surface. 

FIG.  63. 


Dikes  are  met  with  from  a  few  inches  to  more  than  a  mile  in  thickness. 
Ill  volcanic  eruptions  they  may  be  seen  in  the  process  of  formation,  as  deep 
rents  and  fissures  filled  with  liquid  lava.  Fig.  64  represents  dikes  of  modern 
lava  traversing  rocks  in  the  vicinity  of  Mt.  Etna. 

Yery  fine  examples  of  trap-dikes  may  bo  found  in  all  the  trap  districts  of 
FiG.  64. 


VEINS     AND      DIKES. 


97 


New  England ;  and  on  the  coast  of  Massachusetts  Bay — especially  at  Lynn, 
Marblehead,  Beverly,  Salem,  Cohasset,  and  Nahant — the  rocks  are  every- 
where traversed  with  dikes  of  trap  and  porphyry.  One  dike,  near  Pulpit- 
Rock,  at  Xahant,  is  over  thirty  feet  in  width.* 

Veins  and  dikes  frequently  intersect ;  and,  in  such  cases,  the  one  which 
cuts  through  the  other  must  be  regarded  as  the  last  erupted.  In  this  way 
we  are  able  to  demonstrate  the  eruption  of  igneous  rocks  at  several  success- 
ive and  distinct  epochs.  Pig.  65  represents  an  interesting  example  of  dykes 
of  trap  and  porphyry,  erupted  at  four  different  periods,  in  the  syenitie  recks 
of  Cohasset,  Massachusetts.  The  base  of  tho  rock  1  being  syenite;  a  repre- 
sents a  dyke  of  porphyry  ten  feet  in  width  ;  I,  a  dike  of  greenstone  twenty 
feet  wide ;  c,  c,  c,  three  smaller  dykes  of  greenstone,  of  a  darker  color.  In 

FIG.  G5. 


tins  case  wo  have,  undisputably,  tho  following  record  of  events:  First,  the 
formation  of  the  syenite ;  second,  the  syenite  was  rent,  and  tho  fissure  filled 
with  melted  porphyry;  third,  the  syenite  was  rent  across  tho  porphyry,  and: 
molten  trap  flowed  up,  forming  a  dike  twenty  feet  wide ;  and,  finally,  three 
fissures  were  formed  across  the  large  dike,  which  were  subsequently  filled 
with  trap  of  a  somewhat  different  composition.  In  this  example,  further- 
more, it  will  bo  observed  that  portions  of  the  syenite  are  imbedded  between 

QUESTIONS. — What  are  some  examples  of  remarkable  dikes?  How  may  we  determine 
the  relative  age  of  intersecting  veir.s  and  dikes? 

*  One  of  the  most  wonderful  examples  of  a  trap-dike  exists  in  the  coal  fields  of  the 
north  of  England,  and  is  known  as  the  "Cookfield  Fell  Dike."  It  consists  of  a  nearly 
vertical  wall  of  trap,  eighteen  or  twenty  yards  thick,  which  runs  in  a  nearly  straight  line 
for  a  distance  of  about  seventy  miles.  In  one  instance,  where  it  crosses  a  bed  of  coal,  tho 
coal  for  a  distance  of  eight  yards  from  it  is  converted  into  a  kind  of  cinder,  while  lime- 
stones, and  other  rocks  in  contact  with  it,  appear  as  if  they  had  been  baked. 

5 


98 


FIRST     PRINCIPLES     OF     GEOLOGY. 


the  smaller  dikes  upon  the  right  of  the  engraving,  and  these  imbedded  masses 
masses  present  evidence  of  having  been  inclosed  by  the  trap,  while  the  latter 
was  in  a  state  of  fusion. 

108.  Veins  of  Segregation,— In  some  instances  veins  arc 
found  entirely  included  or  insulated  in  the  rock,  and  can- 
not be  traced  «to  a  connection  with  any  larger  mass  of  simi- 
lar character.  Such  veins,  in  general,  appear  to  have  been 
formed  of  materials  which  have  been  separated  or  segre- 
gated by  chemical  action  from  the  mass  of  the  containing 
rock,  and  pass  at  their  edges,  by  insensible  gradations,  into 
that  rock.  They  are,  hence,  termed  "  veins  of  segregation." 

FIG.  66. 


In  other  instances,  veins  have  undoubtedly  been  formed  by  the  deposition 
of  mineral  matter  from  aqueous  solutions  trickling  through,  or  filling  up  rock- 
fissures.  In  this  way  many  veins  of  carbonate  of  lime,  in  slates  and  shales, 
have  probably  originated.  Fig.  66  is  a  representation  (from  a  photograph) 
of  veins  of  carbonate  of  lime  in  black  slate,  from  the  shores  of  Lake  Cham- 
plain,  Yt. 


CHAPTER    VIII. 

GEOLOGICAL    AGENCIES. 


109.  IP  there  is  any  one  fact  which  the  study  of  geology  teaches  more  un- 
mistakably than  another,  it  is,  that  the  matter  composing  the  crust  of  the 
earth,  from  the  time  when  it  was  first  called  into  existence  by  thofiat  of  the 

QUESTIONS.— What  are  veins  of  segregation  ?  What  one  fact  respecting  the  history  of 
the  earth  does  the  study  of  geology  especially  teach  ? 


GEOLOGICAL      AGENCIES.  99 

Creator  to  the  present,  has  been  subjected  to  an  endless  cycle  of  mutations. 
There  may  have  been  periods  of  comparative  rest  and  quiescence,  but  none 
of  perfect  stagnation  and  stability ;  so  that  the  present  condition  and  con- 
figuration of  the  earth's  surface  may  be  considered  as  the  last  result  of  a 
series  of  cosrnical  changes,  which  commenced  with  the  dawn  of  creation,  and 
are  continuing  on  into  the  future. 

"  Had  the  exterior  crust  of  the  earth  been  subjected  to  no  modifying  causes, 
the  world  would  have  presented  the  same  appearance  now  as  at  the  time  of 
its  creation.  The  distribution  of  land  and  sea  would  have  remained  the  same ; 
there  would  have  been  the  same  surface  arrangement  of  hill,  valley,  and  plain, 
and  the  same  unvarying  aspects  of  animal  and  vegetable  existence.  Under 
such  circumstances,  geology,  instead  of  striving  to  present  a  consecutive  his- 
tory of  change  and  progress,  would  have  been  limited  to  a  mere  description  of 
permanently  enduring  appearances.  The  case,  however,  is  widely  different." 
There  is  no  part  of  the  present  land-surfaco  of  the  globe  which  has  not  at 
some  time  been  covered  by  the  ocean,  while  much  of  the  present  sea-bottom 
lia-s  been  in  turn  dry  land.  Many  of  the  loftiest  and  most  extensive  ranges 
of  mountains  upon  the  globe — the  Alps,  the  Andes,  and  the  Himalayas — are 
of  comparatively  recent  elevation  (recent  as  compared  with  the  White  Moun- 
tains of  New  England,  or  the  Appalachian  chain  of  the  Atlantic  States) ;  while 
the  commencement  of  the  existence  of  every  animal  and  vegetable  species  at 
present  found  upon  the  earth  was  long  subsequent  to  the  existence  of  the 
myriad  organisms,  whose  remains  are  now  found  fossil  beneath  its  surface. 

The  agencies  which  have  produced,  and  are  still  tend- 
ing to  produce,  changes  in  the  constitution  and  structure 
of  our  planet,  may  be  classified  as  follows  :  1.  Igneous 
agencies,  or  such  as  manifest  themselves  in  connection  with 
some  deep-seated  source  of  heat  in  the  interior  of  the  globe. 
2.  Aqueous,  or  those  arising  from  the  action  of  water.  3. 
Atmospheric,  or  those  operating  through  the  medium  of  the 
atmosphere.  4.  Organic,  or  those  depending  on  animal 
and  vegetable  growth.  5.  Chemical,  or  those  resulting 
from  the  chemical  action  of  substances  on  each  other. 

s  E  c  T  I  0  X    I . 

IGNEOUS      AGENCIES. 

110.  From  what  has  been  already  said  respecting  the  origin  of  certain 
rocks,  the  student  must  have  inferred  that  geologists  recognize  heat  as  one 
of  the  great  agencies  which,  in  times  past,  have  been  active  in  determining 

QUESTIONS.— What  would  have  been  the  condition  of  the  earth's  surface  had  it  re- 
mained unchanged?  What  are  the  agencies  concerned  in  producing  geological  changes  ? 

^ 


100       FIRST      PRINCIPLES     OF     GEOLOGY. 

the  constitution  and  structure  of  our  planet.  And  no  person  at  the  present 
time  can  witness,  or  even  read  of,  the  eruption  of  a  volcano,  or,  to  choose  a 
more  familiar  illustration,  can  observe  the  constant  supply  of  heated  waters 
that  flow  from  the  numerous  warm  springs  of  our  own  country,  without  being 
forcibly  impressed  with  the  idea  that  heat  is  still  a  most  active  element  in  the 
earth's  crust,  at  no  great  distance  beneath  its  surface.  When  examined  in 
detail  the  evidence  is  much  more  conclusive. 

111.  Temperature  of  the  Earth. — If  we  descend  beneath 
the  surface  of  the  earth,  and  observe  the  temperature  with 
a  thermometer  at  different  depths,  it  will  be  found  that, 
at  a  certain  depth,  the  thermometer  remains  stationary, 
and  is  uninfluenced  by  either  the  heat  of  summer  or  the 
cold  of  winter.  This  depth,  called  the  "stratum  of  in- 
variable temperature/'  ranges,  in  the  temperate  zones,  at 
from  fifty  to  ninety  feet  below  the  surface,  according  as 
the  material  passed  through  is  rock,  clay,  sand,  or  water. 
Below  this  depth,  the  temperature  increases  as  we  descend, 
at  the  rate  of  one  degree  of  Fahrenheit  for  every  fifty  or 
sixty  feet  of  descent  *  Experiments  made  in  various  deep 
mines  and  artesian  wells  have  invariably  shown  this  to  be 
the  case  in  all  quarters  of  the  globe  and  in  all  kinds  of 
rock. 

Now,  if  this  increase  of  heat  toward  the  center  goes  on  at  the  same  rate 
that  it  does  near  the  surface,  the  temperature,  at  a  depth  of  9000  feet  (about 
one  and  three  quarters  miles),  must  equal  that  of  boiling  water,  and,  at  the 

QUESTIONS. — "What  influence  has  heat  exerted  upon  the  structure  of  the  earth  ?  What 
is  the  stratum  of  invariable  temperature  in  the  earth  ?  What  is  its  range? 

*  The  following  are  some  of  the  observations  made  most  recently  on  this  subject:  In 
England  observations  have  been  made  in  the  vertical  shafts  of  two  very  deep  coal  mineb, 
viz.,  at  Monkwearmouth,  which  is  1800  feet  deep,  and  Dunkinfield,  which  is  upwards  of 
2000  feet  deep,  and  in  both  cases  the  observations  were  made  whilo  the  workmen  were 
sinking  the  shafts,  and  with  every  precaution  against  the  influence  of  any  extraneous 
causes.  The  former  gave  an  increase  of  1°  of  Fahrenheit  for  every  sixty  feet  of  depth, 
and  the  latter  1°  for  about  every  seventy  feet.  The  artesian  well  of  Grenelle  (Paris),  is 
1800  feet  deep  ;  observations  made  by  Arago,  during  the  boring,  showed  that  the  average 
increase  of  temperature  in  this  was  1°  for  sixty  feet.  At  Mordorff,  Luxemburg,  the  depth 
of  the  artesian  well  is  2400  feet,  and  the  increase  in  temperature  1°  for  every  fifty-seven 
feet.  At  the  artesian  well  of  New  Scltzwork,  in  Westphalia,  the  depth  is  2100  feet,  and 
the  increase  1°  for  every  fifty-five  feet.  At  Louisville,  Ky.,  the  depth  of  au  artesian  well, 
finished  in  1859,  is  2086  feet  deep,  and  the  average  increase  is  1°  for  every  sixty-seven  feet 
below  the  first  90  feet  from  the  surface.  In  the  silver  mine  of  Guanaxato,  Mexico,  1713 
feet  deep,  the  increase  is  1°  for  every  forty-five,  ft-et,  In  the  coal  jr.ine.s  of  Eastern 
Virginia,  the  average  increase  is  about  V  for  every  sixty  feet. 


IGNEOUS     AGENCIES.  101 

comparatively  small  depth  of  twenty-five  or  thirty  miles,  the  heat  is  probably 
sufficient  to  reduce  to  fusion  any  material  found  upon  the  earth's  surface. 

It  is  also  a  fact  of  much  significance  that  the  waters  of  deep  springs  and 
wells  (such  as  deep  artesian  wells),  have  always  a  high  temperature.  The 
water  of  the  artesian  well  of  Crenelle  (Paris),  1,800  feet  deep,  has  a  con- 
stant temperature  of  82°  F.,  while  the  mean  temperature  of  the  air  in  the 
cellars  cf  the  Observatory  at  Paris  is  only  53°  F.  The  water  of  the  artesian 
well  at  Louisville,  Ky. — 2,086  feet  deep — as  it  flows  from  the  top,  has  a  con- 
stant temperature  of  76£°  F.,  and  of  82°  F.  at  the  bottom.  This  well  dis- 
charges at  the  rate  of  220  gallons  per  minute,  consequently  the  source  of  the 
supply  of  heat  to  the  water  cannot  be  local  or  insignificant. 

"As  another  result  of  direct  observation,  we  may  state  that  all  igneous 
rocks  proceed  from  below  upward,  coming  out  of  the  interior  of  the  earth ; 
and  that  whenever  we  are  able  to  see  the  actual  base  of  the  aqueous  rocks  of 
any  district,  we  find  them  reposing  upon  cooled  igneous  rocks,  generally 
granite;  and  that,  celeris  paribus,  the  lower  the  rocks  or  the  deeper 'they 
have  formerly  been  buried,  the  more  marks  do  they  bear  of  having  been  sub- 
jected to  great  heat." — JUKES. 

From  these  and  other  facts,  such  as  the  existence  of 
volcanoes,  and  the  phenomena  of  earthquakes,  which  will 
be  hereafter  noticed,  geologists  have  been  led  very  gener- 
ally to  the  conclusion  that  the  solid  or  rocky  crust  of  the 
earth  forms  but  a  comparatively  thin  film  or  shell,  and 
that  the  great  interior  mass  exists  in  a  state  of  high  in- 
candescence or  molten  fluidity.* 

The  influence  of  such  a  heated  interior  upon  the  present  surface  tempera- 
ture of  the  earth,  is,  however,  insignificant,  owing  to  the  extreme  slowness 
Avith  which  heat  is  transmitted  by  all  earthy  materials.  Supposing  the  ex- 
ternal rocky  crust  to  have  a  thickness  of  thirty  or  forty  miles,  M.  Fourier,  of 

QUESTIONS. — In  what  manner  does  the  temperature  of  the  earth  increase  as  -we  descend 
into  it  ?  What  must  be  the  result  of  a  progressive  increase  of  temperature  ?  What  is 
the  general  temperature  of  deep  springs  and  wells  ?  Give  some  illustrations?  What  ap- 
pears to  have  been  the  source  of  the  igneous  rocks  ?  What  opinion  is  generally  enter- 
tained by  geologists  respecting  the  condition  of  the  interior  of  the  earth  ?  What  effect 
would  a  heated  interior  produce  at  present  upon  the  temperature  of  the  earth's  surface? 


*  Geologists  differ  widely  in  their  estimates  of  the  thickness  of  the  solid  rock-crust  of 
the  earth.  Seme — perhaps  a  majority — are  fnclined  to  the  belief  that  the  most  refractory 
rock- substances  are  in  a  state  of  complete  fusion  at  a  depth  of  twenty  or  thirty  miles: 
others  extend  this  limit  to  sixty  or  eighty  miles.  Mr.  William  Hopkins,  of  England, 
basing  his  conclusions  on  certain  astronomical  phenomena,  and  also  on  the  fact  that  the 
temperature  of  the  melting-point  of  most  substances  is  much  increased  by  great  pressure, 
maintains  that  the  minimum  thickness  of  the  solid  external  crust  of  the  earth  cannot  be 
less  than  800  miles,  although  the  temperature  may  be  at  the  same  time  intense. 


102        FIRST     PRINCIPLES     OF     GEOLOGT. 

Trance,  has  shown,  by  carefully  conducted  experiments  and  mathematical 
reasoning,  that  the  excess  of  temperature  at  the  surface  of  the  earth  from  any 
possible  supply  of  internal  heat  cannot  exceed  r\tli  of  a  degree  of  Fahren- 
heit— an  amount  insufficient  to  melt  a  coating  of  ice  ten  feet  thick  upon  the 
earth's  surface  in  less  than  100  years.* 

It  is,  however,  conceivable,  that  during  the  earlier  geological  epochs  the 
crust  of  the  earth  might  have  been  so  thin  (i.  e.,  before  it  thickened  by  cool- 
ing) as  to  allow  of  the  communication  of  a  large  supply  of  heat  from  the  in- 
terior to  the  surface,  sufficient  even  to  produce  a  tropical  climate  in  extreme 
northern  and  southern  latitudes.  Such  a  supposition,  furthermore,  derives 
some  support  from  the  fact  that  recent  geological  investigations  have  proved, 
that  the  temperature  of  the  Arctic  regions  was  once  sufficiently  elevated  to 
allow  of  the  existence  of  animals  and  plants  analogous  to  those  which  are 
now  found  only  in  the  tropics.f  It  is  not,  however,  probable  that  the  tem- 
perature of  the  earth  has  sensibly  diminished  since  the  commencement  of 
the  historic  period,  or  during  the  last  4,000  years, :{: 

QUESTIONS. — Is  it  conceivable  that  the  surface  temperature  has  been  ever  affected  by 
the  central  heat  of  the  earth  ?  Is  there  any  evidence  on  this  point  ? 


*  Earth  and  rock  are  among  the  very  poorest  conductors  of  heat.  If  we  indicate  the 
conducting  power  of  gold  (the  best  heat-conducting  material)  by  100,  the  figures  37.4  will 
express  the  relative  conducting  power  of  iron,  2.8  that  of  marble,  and  1.1  that  of  clay. 
The  non-conducting  properties  of  "plaster  of  Paris"  (gypsum)  are  so  great  that  it  is  al- 
most impossible  to  heat  water  in  a  tin  vessel  whose  sides  and  bottom  are  thinly  coated 
with  this  substance.  In  descriptions  of  volcanic  eruptions  we  are  often  told  of  persons 
walking  with  impunity  upon  the  cooled  surface  of  lava  streams,  while  a  few  inches  below 
the  surface  the  mass  is  still  incandescent,  or  even  fluid.  la  an  eruption  of  Mount  Etna, 
in  1819,  a  lava  sheet  was  observed  to  be  in  motion,  at  the  rate  of  three  feet  per  day, 
nine  months  after  its  discharge  from  the  crater. 

t  In  Greenland,  which  is  at  present  almost  devoid  of  all  vegetation,  fossil  trunks  of 
trees  have  been  found  in  the  coal  formation  over  three  feet  in  diameter.  The  most  abund- 
ant fossils  collected  by  the  parties  engaged  in  the  recent  search  for  Sir  John  Franklin, 
from  the  rock  formations  of  the  extreme  Arctic  latitudes,  were  corals,  and  varieties  of 
shells  and  plants  of  an  eminently  tropical  character.  (See  Appendix  to  McClintock's  Nar- 
rative, 1859.) 

$  From  these  old  ages  we  have  certainly  no  therrnometric  observations,  but  we  have 
information  regarding  the  distribution  of  certain  cultivated  plants,  the  vine,  the  olive, 
etc.,  which  are  very  sensitive  to  changes  of  the  mean  annual  temperature,  and  we  find 
that  these  plants  have  the  same  limits  of  distribution  that  they  had  in  the  times  of 
Abraham  and  Homer,  from  which  we  may  infer  backward  the  consistency  of  the  climate. 
"As  we  may  judge  of  the  uniformity  of  temperature  from  the  unaltered  time  of  vibra- 
tion of  a  pendulum,  so  we  may  also  learn  from  the  unaltered  velocity  of  the  earth  the 
amount  of  stability  in  the  mean  temperature  of  our  globe.  This  insight  into  the  relations 
between  the  length  of  the  day  and  the  heat  of  the  earth  is  the  result  of  one  of  the  most 
brilliant  applications  of  the  knowledge  we  possess  of  the  movements  of  the  heavens  to  tho 
thermic  condition  of  our  planet.  The  rotary  velocity  of  the  earth  depends  on  its  vol- 
ume ;  and  since,  by  the  gradual  cooling  of  the  mass  by  radiation,  the  axis  of  rotation 
would  become  shorter,  the  rotatory  velocity  would  necessarily  increase,  and  the  length  of 
the  day  diminish,  with  a  decrease  of  the  temperature.  From  a  comparison  of  the  secular 
inequalities  in  the  motions  of  tho  moon,  with  the  eclipses  observed  in  ancient  times,  it 


IGNEOUS     AGENCIES.  103 

112.  The  hypothesis  that  the  rock  crust  of  the  eartli  is  only  a  compara- 
tively thin  shell  or  film,  which  has  consolidated  around  a  heated  interior, 
furnishes  a  very  plausible  explanation  of  all  those  geological  phenomena 
which  appear  to  be  either  directly  or  indirectly  the  result  of  igneous  agency ; 
such  as  volcanic  eruptions,  thermal  springs,  earthquakes,  and  the  upheaval 
or  depression  of  extensive  areas  of  the  earth's  surface.     This  theory,  how- 
ever, has  been  rejected  by  some  very  eminent  geologists,  who  have  suggested 
other  explanations  of  the  facts  above  referred  to.     Thus,  some  have  sup- 
posed that  the  interior  of  the  earth  is  composed,  in  part,  of  the  metallic  bases 
of  the  earths  and  alkalies — particularly  potassium,  sodium,    and  calcium — 
which  combine  energetically  with  oxygen  whenever  they  are  brought  in  con- 
tact with  water,  with  the  evolution  of  light  and  heat.     If  to  these  metals 
water  should  occasionally  find  access  through  fissures  in  the  rock-crust  of  the 
earth,  the  heat  generated  might  be  sufficient  to  melt  the  surrounding  mineral 
matters  and  produce  volcanic  and  earthquake  phenomena.     Other  chemical 
reactions,  and  the  agency  of  electricity,  have  also  been  suggested  as  the  cause 
of  the  internal  heat  of  the  earth,  but  none  of  these  theories  have  thus  far  ob- 
tained general  acceptation. 

113.  Number  and  Distribution  of  Volcanoes, — The  num- 
ber of  active  volcanoes  on  the  globe  is  estimated  at  about 
400.* 

Of  this  number  more  than  three-fourths  occupy  the  islands  or  the  shores  of 
the  Pacific  Ocean.  Thus,  over  seventy  volcanoes  exist  on  the  islands  of  the 
Sunda  Group  (Java,  Sumatra,  etc.) ;  seventy-four  in  Kamtschatka  and  on  the 
Aleutian  and  Kurile  Islands ;  twenty-three  on  the  islands  of  Japan ;  thirty- 
four  on  the  Moluccas  and  Phillippine  Islands ;  fifty-four  on  the  west  coast  of 
South  America ;  forty-eight  in  Central  America ;  and  ten  on  the  west  coast  of 
Xorth  America.  Besides  the  volcanoes  which  thus  fringe  the  Pacific,  almost 
all  the  islands  in  the  interior  of  this  ocean,  which  attain  a  considerable  height, 
are  either  of  volcanic  origin  or  are  subject  to  volcanic  eruptions — as  the  Sand- 
wich, Friendly,  Galapagos,  and  Ladrone  Islands. 

The  Atlantic  Ocean  and  Europe  together  number  thirty-seven  volcanoes ; 
of  these,  ten  are  in  the  West  India  Islands,  and  five  in  Southern  Europe  and 
the  Mediterranean.  There  is  no  certainty  of  the  existence  of  any  active  vol- 
cano on  the  continent  of  Africa. 

QUESTIONS.— Of  what  phenomena  does  this  hypothesis  furnish  a  ready  explanation  ? 
Is  the  theory  of  a  heated  interior  to  the  earth  universally  accepted  ?  What  is  said  of  the 
number  and  distribution  of  volcanoes  ?  Where  are  they  mainly  located? 


follows  that  since  the  time  of  Ilipparchus,  that  is,  for  full  2,000  years,  the  length  of  the 
day  has  certainly  not  diminished  by  the  1 -100th  part  of  a  second.  The  decrease  of  the 
mean  heat  of  the  globe  during  a  period  of  2,000  years  has  not,  therefore,  taking  the  ex- 
tremest  limits,  diminished  as  much  as  l-300th  part  of  a  degree  of  Fahrenheit."—  Humboldt. 
*  This  estimate  includes  alt  those  which  exhibit  some  evidence  of  having  been  in  activity 
during  the  historic  period.  If,  however,  we  class  as  active  those  only  which  have  been  in 
a  state  of  eruption,  within  a  comparatively  recent  period,  the  number  is  reduced  to  about 
270. 


104       FIRST     PRINCIPLES     OF     GEOLOGY 


The  most  extreme  limit  ever  reached  by  man  in  the  southern  hemisphere 
also  presents  a  wonderful  example  of  volcanic  fire.  Sir  James  Eoss,  at  a 
point  on  the  coast  of  the  great  Antarctic  continent,  discovered  in  1841  two 
immense  volcanoes,  the  one  extinct,  called  Mt.  Terror ;  the  other,  discharging 
dense  columns  of  black  smoke,  tinged  with  flame,  called  Mt.  Erebus.  The 
latter  was  estimated  at  no  less  than  12,000  feet  above  the  level  of  the  sea, 
and  formed  part  of  a  stupendous  chain  of  mountains  belonging  to  the  new 
continent,  all  of  which  were  apparently  volcanic. 

The  most  active  volcano  in  the  territory  of  the  United  States  is  Mount  St. 
Helens,  on  the  Columbia  River,  in  Oregon.  In  Mexico  there  are  five  active 
volcanoes ;  and  notable  examples  also  occur  in  the  neighboring  TVrest  Indian 
Islands,  at  Gaudaloupe,  St.  Vincent,  and  St.  Christopher. 

FIG.  67. 
__ 


"With  very  few  exceptions,  the  active  volcanoes  of  the  world  are  found 
either  in  islands,  or,  if  on  continents,  in  situations  comparatively  near  the  sea- 
shore. Hence,  it  has  been  inferred  that  proximity  to  the  sea,  and  the  pene- 
tration of  sea-water  to  the  seat  of  igneous  action,  were  essential  for  the 
production  and  continuance  of  volcanic  phenomena.  Huraboldt,  however, 
supposes  that  littoral  (shore)  situations  only  favor  eruptions,  by  forming  the 
margin  of  a  deep  sea  basin,  which,  covered  with  water,  offers  less  resistance 
to  the  subterranean  fire  than  the  interior  continent  covered  with  a  greater 
weight  of  rock-strata. 

QUESTIONS. — What  volcanoes  of  note  exist  in  or  near  the  territory  of  the  United  States  ? 
What  is  said  of  the  proximity  of  volcanoes  to  the  sea-shore  ?  What  inferences  have  been 
drawn  from  this  fact  ? 


IGNEOUS     A*G  E  N  C  I  E  S . 


105 


Volcanoes  are  rarely  isolated,  but  on  the  contrary  are 
almost  always  arranged  in  lines  or  bands,  which  generally 
coincide  with  extensive  ranges  of  mountains.  * 

Such  a  linear  arrangement,  according  to  Humboldt,  suggests  the  idea  that 
volcanoes  are  merely  vents,  located  above  some  far-extended  subterranean 
crack  or  fissure  in  the  crust  of  the  earth,  through  which  the  molten  matter  of 
the  interior  escapes  to  the  surface.  The  existence  of  these  cracks,  also,  may 
be  equally  efficient  in  allowing  water  to  find  access  to  the  interior,  where, 
coming  in  contact  with  heated  substances,  great  volumes  of  steam  and  gas 
would  be  evolved ;  and  these  in  turn  exerting  an  immense  pressure,  may  be 
directly  concerned  in  producing  an  eruption. 

FIG.  68. 


Of  isolated  volcanoes,  disconnected  with  any  other  extensive  elevation  of 
the  earth's  surface,  the  "Peak  of  Tenerifife,"  12,000  feet  high,  is  one  of  the 
most  marked  examples.  (See  Fig.  67.) 

QUESTIONS. — What  is  said  of  the  relations  of  volcanoes  to  each  other  ?  "What  does  such 
a  linear  arrangement  suggest?  What  is  one  of  the  most  remarkable  isolated  volcanoes? 


*  Such  a  band  or  line  of  vents,  for  example,  is  presented  by  the  volcanoes  of  America, 
those  of  the  Andes  and  Rocky  Mountains  being  connected  by  the  Cordilleras  of  Mexico 
and  Guatemala.  Another  remarkable  line  of  volcanoes  commences  with  Alaska,  on  the 
coast  of  Russian  America,  passes  over  the  Aleutian  Islands,  thence  into  Kamtschatka, 
the  Kurilian,  Japanese,  Philippine,  and  Molucca  Islands,  then  turning  passes  through 
Java  and  Sumatra,  and  finally  terminates  with  the  volcano  of  Barren  Island,  in  the  Bay 
of  Bengal. 


106       FIKST     PRINCIPLES     OF     GEOLOGY. 

The  loftiest  volcano  in  the  globe  is  Aconcagua  (one  of  the  Chilian  Andes), 
which  rises  to  the  height  of  23,900  feet.  The  most  beautifully  regular  and 
symmetrical  volcano  is  Cotopaxi,  19,070  feet.  (See  Fig.  68.)* 

Other  volcanoes  exhibit  no  elevated  cone  whatever,  but  are  mere  accumu- 
lations or  hills  of  loose  materials.  Fig.  69  is  a  representation  of  a  low  vol- 
cano on  Barren  Island,  in  the  Bay  of  Bengal. 

FIG.  G9. 


114.  The  proportionate  size  of  the  craters  of  volcanoes  varies  greatly ;  some 
craters,  as  Vesuvius,  being  small  but  distinct,  while  others  are  of  enormous 
magnitude.  Thus,  the  immediate  crater  of  Kilauea,  at  Hawaii,  one  of  the 
Sandwich  Islands  (located  on  a  table-land  3,970  feel  above  the  level  of  the 
sea),  is  a  crescent-shaped  gulf,  1,500  feet  deep,  and  from  seven  to  ten  miles 
in  circumference,  f  At  the  bottom  of  this  crater  are  several  lakes  of  liquid 
lava,  which  at  times  exceed  two  miles  in  circumference.  At  the  great  vol- 
cano of  Pichincha,  in  South  America — 16,000  feet  high — "the  traveler,"  ac- 
cording to  Humboldt,  "  may  look  down  from  the  edge  of  the  crater  on  the 
summits  of  mountains,  which  rise  in  the  sulphureous  atmosphere  from  the 
cavity  beneath  him." 

QUESTIONS. — What  is  the  loftiest  ?  What  the  most  symmetrical  ?  What  is  said  of  the 
size  of  volcanic  craters  ? 


*  The  summit  of  Cotopaxi  rises  far  ahove  the  "line  of  perpetual  snow,"  and  the  prox- 
imity of  an  eruption,  according  to  Humboldt,  is  indicated  "  by  a  sudden  fusion  of  the 
snow  around  the  edges  of  the  cone.  Before  the  smoke  is  visible  in  the  rarefied  strata  of 
air  surrounding  the  summit  and  the  opening  of  the  crater,  the  walls  of  the  cone  are 
sometimes  in  a  state  of  glowing  heat,  when  the  whole  mountain  presents  an  appearance 
of  fearful  and  portentious  blackness." 

t  "  To  give  an  idea  of  the  capacity  of  this  crater,  the  city  of  New  York  might  be  placed 
within  it,  and  when  at  its  bottom  would  hardly  be  noticed.  All  the  usual  ideas  of  vol- 
canic craters  are  dissipated  upon  seeing  it.  There  is  no  elevated  cone,  and  no  igneous 
matter  or  rocks  ejected  beyond  the  rim.  The  banks  appear  as  if  built  of  massive  blocks, 
which  are,  in  places,  clothed  with  ferns,  nourished  by  the  issuing  vapors.  The  bottom,  in 
the  daytime,  looks  like  a  heap  of  smoldering  ruins,  but  at  night  the  immense  pools  of 
cherry-red  liquid  lava,  in  a  state  of  violent  ebullition,  illuminate  the  whole  expanse, 
while  an  illuminated  cloud  hangs  over  the  whole  like  a  vast  canopy."— Narrative  of  tlie 
U.  S.  Exploring  Expedition. 


IGNEOUS     AGENCIES.  107 

115.  Frequency   of   Eruptions. — Only  a  few  volcanoes  are  in  a 
state  of  constant  activity,  and  the  majority  exhibit  their  powers  only  at  dis- 
tant intervals.      The  volcano  of  Stromboli,  one  of  the  Lipari  islands,  is  a 
perpetually  bubbling  caldron  of  heated  lava,  and  its  operations  were  described 
by  writers  antecedent  to  the  Christian  era.      The  great  volcano  of  Kilauea 
(which  is  the  largest  and  most  remarkable  on  the  globe)  is  always  active. 
Several  volcanoes,  in  South  and  Central  America,  are  also  constantly  burn- 
ing; and,  since  the  date  of  the  Spanish  Conquest,  smoke  has  issued  uninter- 
ruptedly from  the  lofty  peak  (IT, 000  feet)  of  Popocatepetl,  in  Mexico. 

On  the  other  hand,  Vesuvius,  which  is  one  of  the  best  known,  although 
one  of  the  smallest  volcanoes,*  is  not  recorded  as  active  before  the  year 
79,  after  the  Christian  era,  when  the  famous  eruption  took  place  which  de- 
stroyed the  cities  of  Herculaneum  and  Pompeii.  After  the  year  1139,  it  re- 
mained dormant  for  168  j^ears.  During  the  interval  between  1500  and  1631 
it  was  also  apparently  extinct,  and  the  interior  of  the  crater  is  described  as 
covered  with  shrubs  and  rich  herbage.  Of  late  years,  however,  Vesuvius 
has  been  exceedingly  active.  The  volcano  of  Ischia,  in  the  Mediterra- 
nean, is  believed  to  have  enjoyed  an  interval  of  rest  for  about  seventeen 
centuries,  or  up  to  1302,  when  an  eruption  broke  forth,  which  lasted  for  two 
months*  From  these  facts,  therefore,  it  is  not  improbable  that  some  of  the 
volcanoes  now  regarded  as  extinct  (like  Chimborazo,  in  South  America,  or 
Mt  Ararat,  in  Eastern  Asia),  may  at  some  future  period  exhibit  intense 
activity. 

The  number  of  volcanic  eruptions  which  take  place  in  a 
century  has  been  estimated  at  2,000,  or  at  the  average 
rate  of  about  twenty  every  year. 

116.  Phenomena  of  an   Eruption. — The  eruptions  from  those  vol- 
canoes, whose  activity  is  intermittent,  resemble  each  other  so  closely  that  the 
history  of  one  is  very  much  that  of  all ;  and  this  similarity  is  not  limited  to  the 
external  circumstances — namely,  the  explosion,  the  darkness,  the  torrents  of 
lava,  mud,  or  water,  and  the  evolution  of  smoke   and  gases — but  equally 
holds  good  in  regard  to  the  nature  of  the  matter  ejected  from  the  interior  of 
the  mountain.     Not*  only  is  the  matter  thrown  out  by  volcanoes  in  the  most 
distant  parts  of  the  world  (with  few  exceptions)  alike  in  form,  but  it  is  almost 
identical  in  chemical  composition.     "Wo  find  that  lava,  scoria3,  ashes,  and  other 
products,  proceed  from  all,  or  almost  all  volcanoes,  and  these  products,  when 
analyzed  by  the  chemist,  yield  nearly  the  same  ultimate  elements. 

QUESTIONS — Are  the  so-called  "active  volcanoes"  always  in  a  state  of  eruption?  Men- 
tion some  of  the  constantly  active  volcanoes  ?  What  is  said  of  the  eruptions  of  Vesuvius  ? 
What  is  the  average  annual  number  of  volcanic  eruptions  ?  What  is  said  of  the  similarity 
of  volcanic  eruptions  ? 

*  The  volcanoes  of  southern  Europe,  in  the  region  of  the  Mediterranean,  being  sur- 
rounded by  long-civilized  communities,  have  been  more  closely  observed  and  studied 
than  any  others  on  the  globe ;  but  the  phenomena  they  exhibit  are  insignificant  when 
compared  with  the  operations  of  the  mighty  volcanoes  of  South  America,  or  those  of  the 
Indian  Archipelago. 


108        FIRST     PRINCIPLES     OF     GEOLOGY. 

Eruptions  are  generally  preceded  by  loud,  subterranean  noises,  and  fre- 
quently by  slight  shocks  of  earthquakes,  Fountains  and  springs  dry  up,  and 
the  air,  pervaded  by  an  unnatural  stillness,  seems  close  and  oppressive.  The 
sounds  are  described  as  being  sometimes  of  the  most  awful  description,  and 
the  noise,  according  to  some  writers,  resembling  discharges  of  heavy  artillery, 
and  awful  roarings.*  At  the  time  when  these  sounds  arc  issuing  from  beneath 
the  ground,  columns  of  dense  smoke  are  seen  to  issue  from  the  crater  of  the  vol- 
cano. This  smoke  occasionally  assumes  a  very  singular  appearance,  and  bears 
some  resemblance  to  a  tree,  or  an  open  umbrella.  It  sometimes  overhangs 
so  great  an  area  as  to  produce  total  darkness  in  the  neighborhood  of  the 
volcano,  and  is  then  accompanied  by  a  fall  of  volcanic  sand  and  ashes,  which 
often  attain  a  considerable  depth,  f 

Succeeding  the  smoke,  immense  quantities  of  stones,  of  different  sizes, 
mixed  with  ashes  and  sand,  are  now  cast  up  from  the  mouth  of  the  crater. 
In  the  eruption  of  Mt.  Vesuvius,  in  1779,  a  huge  red  column  of  liquid  lava, 
mixed  with  stones,  was  projected  to  a  height,  according  to  Sir  "William 
Hamilton,  of  10,000  feet ;  and  the  flames  of  Cotopaxi,  according  to  Humboldt, 
have  risen  2,700  feet  above  the  crater. 

The  eruption  generally  soon  reaches  the  point  at  which  the  molten  lava 
begins  to  flow  either  over  the  crater  or  from  lateral  vents.  It  issues  in  a 
dark,  sluggish  stream,  being  sometimes  of  great  breadth  and  depth,  and  always 
carrying  destruction  in  its  path4  Fig.  70  represents  the  appearance  of  a 
lava  stream  as  it  flows  from  the  crater  of  Vesuvius. 

QUESTION. — Describe-the  phenomena  of  an  eruption. 


*  Humboldt  mentions  that  the  ceilings  in  the  palace  at  Portici,  at  the  foot  of  Mt. 
Vesuvius,  were  cracked  by  the  mere  effect  of  the  concussion  of  the  air.  On  the  occasion 
of  an  eruption  of  the  volcano  of  Cozeguina,  in  Central  America,  the  explosions  are  said  to 
have  been  heard  over  an  area  of  nearly  1,500  miles  in  diameter.  During  an  eruption  in 
Sumbawa,  one  of  the  Sunda  Islands,  the  sounds  were  heard  in  Sumatra,  at  a  distance  of 
of  970  geographical  miles,  and  at  Ternate,  in  an  opposite  direction,  at  a  distance  of  72l> 
,  miles. 

t  At  the  eruption  of  Cozeguina,  in  Central  America,  in  1835,  the  sand  and  ashes  fell  in 
such  quantities  in  the  immediate  vicinity  as  to  crush  in  the  roofs  of  houses ;  ashes  also  fell 
at  Leon,  more  than  100  miles  distant,  to  the  depth  of  several  inches,  and  in  Jamaica  and 
Vera  Cruz,  comprising  an  area,  in  all,  of  1,500  miles  in  diameter. — Squier's  Nicaragua. 
It  was  by  showers  of  this  kind  that  the  Italian  cities  of  Pompeii  and  Herculaneum  were 
buried  in  the  year  79  of  the  Christian  Era.  In  this  cass,  however,  the  fine,  loose  materials 
appear  to  have  been  in  part  converted  into  mud  by  copious  showers  of  rain,  which  resulted 
from  the  condensation  of  the  vapors  ejected  from  the  volcano ;  and  hence,  as  these  cities  are 
excavated,  everything  enveloped  is  found  in  a  most  perfect  state  of  preservation— the 
pavements,  with  the  carriage  ruts  in  them,  still  distinct;  the  fresco-paintings  on  tho 
walls  almost  as  vivid  as  if  just  finished ;  the  fabrics  in  the  shops  still  showing  their  text- 
ure ;  bread  retaining  the  stamp  of  the  baker ;  and  rolls  of  manuscript  with  the  writing 
still  legible. 

$  At  an  eruption  of  Mt.  Etna,  in  1792,  it  is  mentioned  that  the  liquid  lava  streams  were 
often  thirty  feet  high  ;  and,  when  confined  in  narrow  channels,  they  reached  a  height  of 
300  feet.  Lava  streams  of  the  depth  of  100  feet  have  repeatedly  flowed  from  volcanoes 
in  Iceland. 


IGNEOUS     AGENCIES. 
FIG.  70. 


109 


The  progress  of  the  lava  is  generally  very  slow;  the  rate  of  speed  differing 
according  as  the  lava-stream  descends  a  more  or  less  inclined  surface.  At 
the  great  eruption  of  Mauna  Loa,  Sandwich  Islands,  in  1859,  a  lava  stream 
from  an  eighth  to  a  half  a  mile  in  width,  ran  twentj'-five  miles  in  a  single  night, 
but  did  not  reach  the  sea,  forty  miles  distant  from  the  crater,  until  eight  days 
after  the  commencement  of  the  eruption.  Its  speed  at  some  points  near  the 
crater  was  estimated  at  thirty  miles  and  upward  per  hour.  It  has  been  ob- 
served that  lava,  springing  from  a  low  source,  is  generally  in  a  more  liquid 
state  than  that  from  a  more  elevated  crater ;  and  that  craters  of  low  eleva- 
tion throw  out  a  much  greater  quantity  of  lava.  The  highest  volcanoes  of 
South  America  do  not  at  present  discharge  any  lava. 

In  the  place  of  lava,  torrents  of  mud,  flowing  with  great  violence,  are  some- 
times the  accompaniment  of  volcanic  eruptions.  Mud  torrents,  from  Mt. 
Carguairazo,  in  South  America,  are  said,  on  one  occasion,  to  have  covered  a 
surface  of  about  forty  miles  square ;  and  similar  streams,  from  Tunguragua, 
near  Quito,  S.  A.  (in  1797),  filled  valleys  1,000  feet  wide  to  the  depth  of  600 
feet. 

From  some  volcanic  fissures  mud  and  steam  are  the  principal  products 
ejected.  Very  curious  examples  of  this  nature  have  been  recently  discovered 
in  the  Colorado  Desert,  on  the  eastern  borders  of  California.  

QUESTIONS.— What  is  said  of  the  progress  and  depth  of  lava  streams?  What  other 
products  besides  lava  are  emitted  from  volcanic  openings  ? 


110      FIRST     PRINCIPLES      OF     GEOLOGY. 

Other  volcanic  fissures,  or  vents,  are  remarkable  for  the  discharge  of  sul- 
phurous vapors,  and  carbonic  acid  or  other  gases.  A  crater  on  the  Island  of 
Java  contains  a  lake,  strongly  impregnated  with  sulphuric  acid,  a  quarter  of 
a  mile  long,  from  which  a  river  of  acid  water  issues,  which  supports  no  living 
creature,  nor  can  fish  live  in  the  sea  near  its  confluence.  The  famous  "  Valley 
of  the  Upas  Tree,"  or  the  "Valley  of  Death,"  in  Java,  is  simply  the  crater  of 
an  extinct  volcano,  half  a  mile  in  circumference,  filled  with  carbonic  acid  gas, 
which  continually  emanates  from  fissures  in  the  bottom  of  the  valley.  The 
gas  being  invisible,  and  entirely  irrespirable,  every  living  thing  that  descends 
below  the  margin  of  the  valley  is  instantly  suffocated ;  and  as  the  same  fate 
awaits  any  one  that  may  go  to  the  rescue,  the  ground  is  covered  with  the 
bones  of  numerous  animals,  and  even  men,  that  have  approached  the  pre- 
cincts. The  deadly  influence  of  this  valley  was  formerly  ascribed  to  the 
malignant  properties  of  a  peculiar  vegetable  production  of  the  island,  called 
the  "upas  tree,"  which  especially  flourishes  in  this  locality. 

117.  Submarine   Volcanoes . — Volcanic  eruptions  take  place  as  well 
beneath  the  waters  of  the  ocean  as  upon  the  land,  although  opportunities 
for  observing  such  phenomena  are  not  as  frequent.     The  crews  of  vessels 
have,  however,  sometimes  reported  that  they  have  seen  in  different  places 
sulphurous  smoke,  flame,  jets  of  water  or  of  steam,  rising  up  from  the  sea,  or 
they  have  encountered  islands,  or  reefs  of  rocks  emerging  above  the  sur- 
face of  the  ocean,  where  previously  there  was  always  supposed  to  be  deep 
water.     In  1811,  a  violent  submarine  eruption  (see  Fig.  71)  was  observed  in 
the  vicinity  of  the  Azores,  and  resulted  in  the  formation  of  an  island  300  feet 
high,  and  a  mile  in  circumference,  which,  after  a  time,  disappeared.     In  1814, 
a  volcanic  peak,  3,000  feet  high,  was  protruded  above  the  ocean,  in  the  vicin- 
ity of  the  Aleutian  Islands,  east  ofKamtschatka.     In  1831,  a  volcanic  island, 
called  Graham's  Island,  one  and  a  third  miles  in  circumference,  and  about 
200  feet  high,  rose  in  the  Mediterranean,  off  the  coast  of  Sicily.     This  island 
lasted  about  three  years,  when  it  was  washed  away,  leaving  an  extensive 
shoal  in  its  place.     The  water  in  this  locality,  previous  to  the  eruption,  was 
known  to  have  been  600  feet  deep. 

118.  One  or  two  remarkable  instances  of  volcanic  eruptions  may  be  briefly 
noticed.     First,  for  duration  and  force  we  may  refer  to  that  which  took  place 
in  the  island  of  Sumbawa  (one  of  the  Sunda  Islands  lying  east  of  Java),  in 
the  year  1815.     It  commenced  on  the  5th  of  April,  and  did  not  entirely  cease 
until  July.     Its  influence  (i.  e.,  shocks,  and  the  noise  of  the  explosions)  was 
perceptible  over  an  area  1,800  miles  in  diameter,  while  within  the  range  of 
its  more  immediate  vicinity,  embracing  a  space  of  400  miles,  its  effects  were 
most  terrific.     In  Java,  300  miles  distant,  it  seemed  to  be  awfully  present. 
The  sky  was  overcast  at  noon-day  with  clouds  of  ashes,  which  the  light  of 
the  sun  was  unable  to  penetrate,  and  fields,  streets,  and  houses  were  covered 

QUESTIONS. — Mention  some  examples?  Do  volcanic  eruptions  take  place  on  the  bed 
of  the  ocean  ?  Mention  some  of  the  incidents  attending  such  eruptions? 


IGNEOUS     AGENCIES. 

FIG.  71. 


Ill 


with  ashes  'to  the  depth  of  several  inches.  At  Sumbawa  itself,  immense  col- 
umns of  flame  appeared  to  burst  forth  from  the  top  of  the  volcano,  Tombora, 
and  in  a  short  time  the  whole  mountain  appeared  like  a  mass  of  liquid  fire, 
which  gradually  extended  in  every  direction.  As  the  eruption  continued,  a 
darkness  supervened,  so  profound  as  to  obscure  even  the  light  of  the  flames ; 
showers  of  stones  and  ashes  fell  continuously  over  the  whole  island  ;  the  sea 
rose  twelve  feet  higher  than  it  had  ever  been  known  to  do  before ;  and  finally 
a  whirlwind  ensued,  which  tore  up  the  largest  trees,  and  carried  them  into 
the  air,  together  with  men  horses,  cattle,  and  whatever  else  came  within  its 
influence.  Of  12,000  inhabitants  in  the  vicinity  only  six  are  believed  to  have 
escaped,  and  of  some  entire  villages  not  even  a  vestige  remained. 

In  1772,  the  Papaudayang,  one  of  the  loftiest  volcanic  mountains  in  Java, 
after  a  short  but  severe  eruption,  suddenly  fell  in  and  disappeared  in  the 
earth,  carrying  with  it  about  ninety  square  miles  of  territory.  Forty  villages 
were  engulfed,  or  covered  with  ejected  matter,  at  the  same  time,  and  nearly 
3,000  persons  perished. 

Another  eruption  worthy  of  mention,  in  respect  to  the  quantity  of  lava 
ejected,  was  that  of  one  of  the  volcanoes  of  Iceland — the  Skaptar  Jokul — in 
the  year  1783.  This  eruption  commenced  in  May  and  lasted  until  the  end 
of  August,  during  the  greater  part  of  which  time  the  sun  was  entirely  hid  by 
dense  clouds  of  ashes  and  vapors,  which  extended  even  to  England  and 

QUESTION. — What  are  some  of  the  most  remarkable  volcanic  eruptions  on  record  ? 


112      FIRST     PRINCIPLES     OF     GEOLOGY. 

Holland.  The  lava  flowed  from  the  volcano  for  ten  weeks  in  two  nearly  op- 
posite streams,  each  of  which  had  a  length  of  about  fifty  miles,  with  a  vary- 
ing breadth  of  from  seven  to  fifteen  miles.  The  thickness  of  these  streams 
was  variable,  being  from  500  to  600  feet  in  the  narrow  channels,  but  in  the 
plains  rarely  more  than  100,  and  often  not  exceeding  ten  feet.  Both  streams 
discharged  into  the  sea,  entirely  destroying  the  fisheries  on  the  coast,  and 
thereby  adding  another  misery  to  the  condition  of  the  poor  inhabitants.  Some 
rivers  upon  the  island  were  heated  to  ebullition;  others  dried  up;  the  con- 
densed vapors  fell  in  snow  and  torrents  of  rain ;  the  whole  country  was  laid 
waste;  famine  and  disease  ensued,  and  in  the  course  of  the  two  following 
years  9,000  human  beings  (one  fifth  of  the  population)  and  immense  numbers 
of  horses,  cattle,  and  sheep  perished.  The  scene  of  horror  was  closed  by  a 
dreadful  earthquake.  Previous  to  the  eruption  an  ominous  mildness  of  tem- 
perature indicated  the  approach  of  the  volcanic  fire  toward  the  surface  of  the 
earth ;  a  warning  which  has  been  observed  in  other  eruptions. 

119.  Force  of  Volcanic  Action. — The  force  exerted  by  volcanic 
agency  is  almost  beyond  computation.  In  the  eruption  of  Skaptur  Jokul, 
above  described,  it  was  estimated  that  there  was  discharged  from  the  bowels 
of  the  earth,  through  this  volcano,  in  the  space  often  weeks,  60,000  millions 
cubic  feet  of  molten  matter,  or  forty  millions  of  tuns.  In  an  eruption  of 
Kilauea,  S.  I.,  in  1840,  Prof.  Dana  estimated  the  amount  of  matter  that 
flowed  out  to  be  equal  to  15,400,000,000  cubic  feet — a  mass  sufficient  to  form 
a  triangular  ridge  two  miles  long,  800  feet  high,  and  a  mile  wide  at  the  base. 
The  projectile  force  occasionally  exerted  in  eruptions,  may  be  judged  of  by 
the  distance  to  which  masses  of  rock  have  been  thrown  from  the  crater  of 
volcanoes.  Thus,  Cotopaxi  on  one  occasion  threw  a  mass  of  rock,  109  cubic 
yards  in  volume,  to  a  distance  of  nine  miles;  and  the  same  volcano  (which  is 
19,000  feet  high)  has  projected  material  6,000  feet  above  its  summit.  Vesu- 
vius also  (3,900  feet  high)  has  also  thrown  scoria  4,000  feet  above  its 
summit. 

The  summit  of  Vesuvius  is  3,900  feet  above  the  sea-level.  Now,  to  force 
a,  column  of  liquid  lava,  of  the  specific  gravity  of  2.8  (the  comparative  weight 
of  compact  marble),  up  the  chimney  of  this  volcano,  to  a  height  sufficient  to 
cause  the  lava  to  flow  over  the  crater,  must  require  a  pressure,  at  the  base 
of  the  column,  of  at  least  4,700  pounds  to  the  square  inch.  In  the  case  of 
Mauna  Loa,  Sandwich  Islands,  which  is  13,600  feet  high,  the  pressure  requi- 
site to  effect  the  same  result  must  be  16,500  pounds  per  square  inch;  and  at 
Cotopaxi,  18,875  feet  high,  upward  of  22,000  pounds.*  But  the  chimney  of 
a  volcano,  in  all  probability,  extends  to  a  very  great  depth — miles  possibly — 

QUESTIONS. — What  is  said  of  the  force  exerted  by  volcanic  agencies?    "What  proofs 
have  •we  of  the  enormous  power  exerted  ? 


*  A  better  idea  of  the  immensity  of  the  power  thus  displayed  may  perhaps  be  gained 
by  remembering  that  the  pressure  used  in  working  high-pressure  steam-engines  dees 
not  ordinarily  exceed  sixty  pounds  per  square  inch  of  the  piston. 


IGNEOUS     AGENCIES.  113 

below  the  sea  level ;  and  hence  the  figures  above  given  must  represent  but 
a  very  small  part  of  the  actual  force  pressing  upon  the  lava  in  its  subter- 
ranean reservoir.  . 

120.  Subterranean   Connection  of  Volcanoes  ,— It  seems  evi- 
dent that  there  exists  in  many  cases  free  communication  under  ground,  be- 
tween volcanoes  at  great  distances  from  each  other.     Thus,  according  to 
Humboldt,  all  the  lofty  volcanoes  in  the  vicinity  of  Quito,  S.  A.,  embracing 
Cotopaxi,  Pichincha,  and  many  others,  are  to  be  viewed  as  the  openings  of 
a  single  volcanic  furnace — the  subterranean  firo  sometimes  breaking  forth 
through  one  and  sometimes  through  another  of  its  chimneys. 

An  open,  subterranean  communication  has  also  been  inferred  to  exist  between 
Etna  and  Vesuvius,  in  Southern  Europe,  since,  when  one  of  these  volcanoes 
is  active,  the  other,  with  all  the  smaller  fissures  in  its  vicinity,  is  generally 
notably  quiet.  In  1183,  when  a  submarine  volcano  on  the  coast  of  Iceland 
ceased  to  eject  matter,  another  immediately  broke  out  180  miles  distant  in 
the  interior  of  the  island.  It  therefore  seems  clear  that  however  distinct  the 
volcanoes  of  the  same  system  may  be  at  the  surface  of  the  earth,  they  are  part 
of  one  general  effect,  produced  by  deep-seated  subterranean  causes. 

121.  Extinct    Volcanoes. — Volcanic  agency  appears  to  have  been 
more  extensive — and  possibly  more  active — in  former  ages  of  the  world  than 
at  present ;  inasmuch  as  the  remains  of  extinct  volcanoes,    craters,   lava- 
streams,  and  accumulations  of  scorias  and  ashes  occupy  extensive  areas  of 
the  earth's  surface,  which  have  exhibited  no  evidence  of  the  action  of  sub- 
terranean fire  during  the  historic  period. 

In  southern  and  central  France  extinct  volcanoes  cover  several  thousand 
square  miles  of  territory,  the  ancient  craters  and  lava  streams  being  every 
way  distinct  and  characteristic.  (See  Fig.  11.)  In  southern  Italy  the  craters 
of  upwards  of  sixty  extinct  volcanoes  can  be  recognized,  some  of  them 
larger  than  Vesuvius.  Extinct  volcanoes  also  exist  in  Spain  and  Portugal, 
in  Germany — along  the  Rhine — in  Hungary,  and  throughout  central  and 
western  Asia,  and  the  whole  peninsula  of  India.  Mt.  Ararat,  in  Armenia, 
is  a  huge  extinct  volcano.  Striking  marks  of  volcanic  action  also  exist 
throughout  Palestine  and  Asia  Minor,  especially  in  the  vicinity  of  Mt.  Sinai 
and  the  Dead  Sea,'- 

In  the  southern  plains  of  South  America  Mr.  Darwin  has  described  a  vast 
deluge  of  lava  which  flowed  in  several  streams  from  the  Andes  to  a  distance 
of  over  100  miles,  and  of  which  the  aggregate  thickness  at  the  extremity  is 
not  less  than  130  feet.  A  large  proportion  of  the  lofty  peaks  of  the  Andes, 
of  the  Cordilleras  in  Mexico  and  California,  and  of  the  Rocky  Mountains,  must 
also  be  included  in  the  class  of  extinct  volcanoes. 

QUESTIONS. — Is  there  any  evidence  of  a  subterranean  connection  between  different  vol- 
canoes ?  What  evidence  have  we  of  volcanic  action  in  former  epochs  of  the  world's  his- 
tory? In  what  countries  are  the  remains  of  extinct  volcanoes  especially  noticeable  ? 

*  The  destruction  of  the  "  Cities  of  the  Plain,"  Sodom  and  Gomorrah,  and  the  forma- 
tion  of  the  Dead  Sea,  is  generally  supposed  by  geologists  to  have  been  the  result  of 
volcanic  action. 


114        FIRST     PRINCIPLES     OF     GEOLOGY. 

122.  Earthquakes  have  been  defined  to  be  volcanoes 
without  any  vent ;  or,  in  other  words,  they  are  the  result 
of  the  action  of  volcanic  forces  confined  beneath  the  earth's 
surface. 

As  the  accidental  bursting  of  a  powder  magazine  is  more  dreadful  than  the 
firing  of  the  heaviest  artillery,  inasmuch  as  the  one  spreads  all  around  and 
the  other  but  in  one  direction,  so  earthquakes  have  ever  inspired  more  terror 
and  been  more  destructive  of  human  life  than  volcanoes. 

Earthquakes  occur  not  only  in  all  volcanic  countries  but 
in  many  districts  which  present  no  mark  whatever  of  vol- 
canic action  and  no  trace  of  volcanic  products. 

123.  Earthquake  Motions,— The  nature  of  the  earth- 
quake shock  is  that  of  waves  propagated  from  a  central 
point  or  focus.* 

These  waves  sometimes  manifest  themselves  as  mere  tremblings  of  the 
earth;  at  other  times,  the  ground  undulates  like  the  sea.  Occasionally  a 
sudden  upward  motion  is  communicated  to  it,  and  when  waves,  advancing  in 
opposite  directions,  cross  each  other,  a  rotary  or  whirling  motion  is  produced. 
Earthquakes  of  the  two  latter  kinds  are  the  most  destructive. 

The  undulations  vary  in  height  from  an  inch  or  two,  to  several  feet.  When 
their  height  is  considerable  very  remarkable  effects  are  produced.  During 
the  terrible  earthquake  which  destroyed  Calabria,  in  Southern  Itaty,  in  1783, 
large  tracts  of  land  were  conveyed  from  their  original  position  to  distances 
of  more  than  half  a  mile.  Humboldt  mentions  that,  on  one  occasion,  furni- 
ture was  carried  from  one  place  and  buried  in  another,  and  some  persons 
were  thrown  across  a  river  to  a  considerable  height  upon  an  opposite  moun- 
tain. 

The  velocity  of  an  earthquake's  wave  varies,  according  to  the  substance 

QUESTIONS. — What  are  earthquakes  ?  Are  earthquakes  more  to  be  apprehended  than 
volcanic  eruptions  ?  Is  the  occurrence  of  earthquakes  limited  to  volcanic  districts  ?  What 
is  the  nature  of  an  earthquake  shock?  What  is  said  of  the  height  of  the  undulations? 
What  of  their  effects  ?  

*  "A  powerful  earthquake,"  says  Mr.  Darwin,  "at  once  destroys  the  oldest  associa- 
tions ;  the  world,  the  very  emblem  of  all  that  is  solid,  has  moved  beneath  our  feet  like  a 
crust  over  a  fluid  :  one  second  of  time  has  conveyed  to  the  mind  a  strange  idea  of  inse- 
curity, which  hours  of  reflection  would  never  have  created." 

"  To  man,"  says  Humboldt,  "  the  earthquake  conveys  an  idea  of  some  universal  and  un- 
limited danger.  We  may  flee  from  the  crater  of  a  volcano  in  active  eruption,  or  from  a 
locality  threatened  by  the  approach  of  a  lava  stream;  but  in  an  earthquake,  direct  our 
flight  whithersover  we  will,  we  still  feel  as  though  we  trod  upon  the  very  focus  of  de- 
struction. Every  sound — the  faintest  motion  in  the  air — arrests  our  attention,  and  we  no 
longer  trust  the  ground  on  which  we  stand.  Animals,  especially  dogs  and  swine,  partici- 
pate in  the  same  anxious  disquietude ;  and  even  crocodiles,  in  the  rivers  of  South  America, 
which  at  other  times  are  dumb,  have  been  observed  to  quit  the  water  and  run,  with  loud 
cries,  into  the  adjacent  forests." 


IGNEOUS      AGENCIES.  115 

through  which  it  is  transmitted.  Some  strata  carry  it  much  further  than 
others ;  and  hence  it  will  be  felt  along  a  particular  line  of  country,  where  the 
stratum  is  more  elastic,  when  it  is  not  perceived  at  places  much  nearer  its 
center.  On  the  land  the  velocity  of  the  wave  has  been  estimated  at  from 
40  to  140  miles  per  minute.  Yery  frequently  earthquakes  originate  in  the 
bed  of  the  ocean,  and  in  such  cases  a  wave  is  generated  in  the  sea  as  well 
as  the  land.  But  the  earth  wave  travels  much  faster  than  the  ocean  wave, 
and  thus  the  destruction  which  the  former  commences  on  a  coast  the  latter 
arrives  to  complete.  The  ocean  wave,  created  by  the  great  earthquake  at 
Lisbon,  in  1755,  traveled  to  the  "West  Indies  at  the  rate  of  about  eight  miles 
per  minute.  In  1854,  a  wave,  caused  by  an  earthquake  in  Japan,  traveled 
across  the  Pacific  to  the  shores  of  California,  in  about  twelve  hours,  or  at  the 
rate  of  about  600  miles  per  hour. 

124.  Earthquakes  are  generally  preceded  by  loud,  rumbling  noises,  and,  in 
great  convulsions,  explosions  like  the  discharges  of  artillery  have  been  heard. 
At  other  times  no  sound  whatever  has  been  recognized. 

125.  Duration  of    Earthquakes,— The  duration  of  an 
earthquake  shock  is  seldom  more  than  a  minute  ;    hut 
successive  shocks  may  succeed  each  other  at  intervals  for 
a  much  longer  period. 

The  great  earthquakes  at  Lisbon,  in  1755,  which  destroyed  60,000  persons, 
lasted  but  five  minutes,  and  the  first  shock  (which  was  the  worst)  but  five  or 
six  seconds.  In  1812  the  city  of  Caracas,  in  South  America,  was  leveled  to 
the  ground  by  three  shocks,  which  occurred  in  the  space  of  fifty  seconds. 

126.  Frequency  of  Earthquakes , — In  some  countries  earthquakes 
of  greater  or  less  intensity  occur  almost  daily.     At  Lima,  in  Peru,  an  aver- 
age of  forty- five  shocks  may  be  expected  yearly;  and  in  Chili  sixty-one  have 
been  noted  in  a  single  year,  without  including  the  slighter  ones.     The  most 
destructive  earthquakes  have  occurred  on  islands  of  the  Indian  Archipelago, 
Southern  Asia ;  on  the  west  coast  of  South  America,  and  in  Southern  Europe, 
in  the  vicinity  of  the  Mediterranean. 

Single  shocks  are  occasionally  felt  in  the  United  States,  east  of  the  Rocky 
Mountains,  but,  with  a  few  exceptions,  their  effects  have  been  inconsider- 
able.* In  Oregon  and  California  earthquake  shocks  are  not  unfrequent. 

QUESTIONS. — What  is  the  velocity  of  earthquake  waves  ?  Do  sounds  precede  the  occur- 
rence of  earthquakes  ?  "What  is  said  of  the  duration  of  earthquakes  ?  What  of  their 
frequency?  In  what  countries  have  the  most  destructive  earthquakes  occurred  ?  Are 
earthquakes  common  in  the  territory  of  the  United  States  ? 


*  In  1811-12,  earthquake  shocks,  experienced  in  the  vicinity  of  New  Madrid,  Missouri, 
caused  the  sinking  of  an  area  of  country  seventy-five  miles  long  by  thirty  wide,  to  a  depth 
of  several  feet.  In  some  places  the  earth  rose  in  great  undulations.  Lakes,  twenty 
miles  in  extent,  were  formed,  while  others  were  drained.  Extensive  fissures  in  the  earth 
Opened,  from  which  columns  of  water,  gravel,  and  mud  were  ejected  to  a  great  height. 
New  islands  also  appeared  in  the  Mississippi.  Some  evidences  of  this  earthquake  are 
even  now  visible. 


116 


FIRST     PRINCIPLES     OF     GEOLOGY. 


The  total  number  of  earthquakes  recorded,  from  the  commencement  of  the 
nineteenth  century  to  the  end  of  the  year  1850,  is  3,240;  of  this  number 
fifty-three  may  be  called  great  earthquakes,  in  which  whole  cities  and  towns 
were  destroyed  and  many  lives  lost 

127.  Remarkable  Earthquakes, — As  illustrative  of  the  effects  of 
earthquakes,  a  few  remarkable  examples  may  be  referred  to 

The  most  dreadful  one  on  record  is  that,  which  in  November,  1755,  de- 
stroyed the  city  of  Lisbon,  in  Portugal.  The  only  warning  the  inhabitants 
received  was  a  noise  like  subterranean  thunder,  which,  without  any  con- 
siderable interval,  was  followed  by  a  succession  of  shocks,  which  laid  in  ruins 
almost  every  building  in  the  city,  with  a  most  incredible  slaughter  of  the  in- 
habitants (60,000).  The  bed  of  the  river  Tagus  was  in  many  places  raised  to 
the  surface,  and  vessels  on  the  river  suddenly  found  themselves  aground. 

FIG.  72. 


The  waters  of  the  river  and  the  sea  at  first  retreated,  and  then  immediately 
rolled  violently  in  upon  the  land,  forming  a  wave  over  fifty  feet  in  elevation. 
To  complete  the  destruction,  a  large  quay,  upon  which  great  numbers  of 
people  had  assembled  for  security,  suddenly  sunk  to  such  an  unfathomable 
depth  that  not  so  much  as  one  body  ever  afterwards  appeared  at  the  surface. 

This  'earthquake  also  affords  the  best  example  on  record  of  the  extent  of 
ground  over  which  some  of  these  great  natural  convulsions  diffuse  them- 
selves;— its  influence  being  felt  over  nearly  4,000,000  square  miles  of  the 
earth's  surface,  and  over  one  twelfth  of  its  circumference.  All  the  islands  of 
the  West  Indies  were  agitated,  and  the  sea  around  them  rose  to  an  unusual 
height ;  the  shock  was  also  perceptible  throughout  New  England  and  the 


IGNEOUS     AGENCIES.  117 

Atlantic  States.  In  Scotland,  Sweden,  and  Norway  the  waters  of  lakes  were 
observed  to  be  in  a  state  of"  commotion,  and  in  many  places  springs  tempor- 
arily disappeared.  In  the  kingdom  of  Morocco  upwards  of  8,000  persons 
perished.  It  was  also  noticed  that  Vesuvius,  which  had  shown  signs  of  erup- 
tion previously,  became  tranquil  at  the  time  of  this  earthquake. 

An  earthquake  which  occurred  in  Calabria,  Southern  Italy,  in  1783,  was 
only  equaled  by  that  of  Lisbon.  It  did  not,  however,  extend  like  the  latter, 
over  so  great  an  area  of  country,  but  the  effects  produced  within  a  limited 
space  were  greater.  Its  duration  was  only  two  minutes,  during  which  time 
it  destroyed  all  the  towns  and  villages  within  a  circuit  of  twenty-two  miles, 
and,  directly  or  indirectly,  the  lives  of  about  100,000  of  the  inhabitants.* 
One  singular  phenomenon  attending  this  earthquake  was  the  formation,  in  the 
earth,  of  singular  cavities,  a  few  feet  in  diameter,  and  in  the  form  of  an  in- 
verted cone,  through  which  a  jet  of  water  spouted.  (See  Fig.  72.) 

A  terrible  earthquake  also  occurred  in  the  kingdom  of  Naples,  in  Decem- 
ber, 1857,  by  which  upward  of  20,000  persons  were  destroyed  in  the  space 
of  a  few  seconds. f 

128.  Theory  of  Earthquakes, — An  examination  of  a  great  number 
of  earthquakes  seems  to  establish  the  fact  that  these  convulsions  occur  more 
frequently  during  the  winter  half  of  the  year  than  during  the  summer  half; 
and  that  there  is  also  a  preponderance  of  shocks  at  the  equinoxes  and  the 
summer  solstice.  Earthquake  action  also  appears  to  be  the  greatest  when 
the  height  of  the  column  of  mercury  in  the  barometer  is  least  (i  e.,  when  the 
atmospheric  pressure  is  least),  and  when  its  range  of  oscillation  is  greatest — 
thus  indicating  that  a  variation  in  the  pressure  of  the  atmosphere  may  have 
some  connection  with  the  phenomenon. 

M.  Perrey,  of  France,  who  has  tabulated  about  7,000  earthquakes,  inclines 
to  the  following  theory  respecting  their  origin :  Starting  with  the  supposition 
that  the  interior  of  the  earth  is  in  a  liquid  or  melted  state,  surrounded  with  a 
comparatively  thin  crust ;  then  the  interior  mass,  being  deprived  of  solidity, 
would  be  compelled  to  yield,  like  the  superficial  mass  of  the  ocean  waters  to 
the  attractive  influence  of  the  sun  and  moon,  and  acquire  a  tendency  to  swell 

QUESTIONS. — Describe  the  effects  of  some  of  the  most  remarkable  earthquakes.  What 
facts  seem  to  be  established  respecting  the  occurrence  of  earthquakes?  What  theory 
lias  been  proposed  by  M.  Perrey,  of  France  ? 


*  The  peninsula  of  Calabria,  where  this  earthquake  occurred,  forms  the  southern  ex- 
tremity of  Italy,  and  is  about  sixty  miles  in  length  by  about  twenty  in  breadth.  Through 
the  center  of  the  peninsula  runs  a  chain  of  granite  mountains,  which  is  separated  from 
the  sea  on  its  western  side  by  a  plain  of  recent  strata,  composed  of  very  yielding  material. 
The  effect  of  the  earthquake  was  to  disconnect,  throughout  almost  the  whole  length  of 
tliis  chain,  the  new  from  the  ancient  rock,  leaving  a  chasm  between  them.  One  half 
of  the  peninsula,  therefore,  actually  slid  in  the  direction  of  the  eea;  and  from  this  fact 
iilone  the  change  and  destruction  consequent  may  be  inferred. 

t  It  appears  from  reliable  data  that  the  kingdom  of  Naples,  in  the  course  of  seventy- 
five  years,  or  from  1783  to  1859,  has  lost,  by  earthquake  agencies,  at  least  110,000  in- 
habitants, or  more  than  1 ,500  per  year,  out  of  an  average  population  of  6,000,000. 


118          FIRST     PRINCIPLES     OF     GEOLOGY. 

out  in  the  direction  of  the  rays  of  these  two  bodies.  This  tendency,  meeting 
with  resistance  from  the  rigidity  of  the  solid  crust,  would  occasion,  shocks 
and  fractures  in  the  latter.  This  theory  is,  however,  opposed,  first,  on  the 
ground  that  if  tidal  movements  do  take  place  in  the  interior  of  the  earth  their 
influence  would  be  not  only  insignificant  as  compared  with  the  total  mass 
of  the  earth,  but  far  within  the  elastic  limits  of  the  earth's  materials ;  and, 
secondly,  that  the  existence  of  a  fluid  interior  to  the  earth  is  but  an  hypothesis. 

On  the  other  hand,  no  satisfactory  hypothesis,  explanatory  of  earthquake 
phenomena,  has  thus  far  been  presented  by  any  geologist  who  rejects  the 
"internal  heat  theory."* 

But  whatever  may  be  the  ultimate  cause  of  earthquakes  and  volcanoes, 
the  supposition  that  they  have  a  common  origin  is  sustained  by  a  great  variety 
of  evidence.  Thus,  it  is  said  to  be  the  general  opinion  at  Naples  and  in 
Sicily,  that  earthquakes  are  not  to  be  dreaded  so  long  as  smoke  escapes 
freely  from  the  craters  of  Vesuvius  and  Etna.  The  same  feeling  also  prevails 
in  the  volcanic  district  of  South  America.  It  is  stated  by  Humboldt  that  the 
volcano  of  Pasto,  in  South  America,  which  for  many  months  had  uninterrupt- 
edly emitted  a  column  of  thick  smoke,  ceased  to  do  so  at  the  very  moment 
that  the  province  of  Quito,  192  miles  to  the  south,  was  convulsed  by  an 
earthquake.  At  the  same  hour  that  the  town  of  Concepcion,  in  Chili,  was 
destroyed  by  an  earthquake,  in  1835,  a  whole  line  of  volcanoes,  situated  in 
the  Andes,  in  the  vicinity,  instantaneously  spouted  out  a  dark  column  of 
smoke ;  and  during  the  time  that  these  eruptions  lasted  (ah1  the  subsequent 
year),  the  immediate  neighborhood  was  entirely  free  from  earthquakes. 

129.  Thermal  Springs, — The  phenomena  of  thermal 
springs  are  attributed  to  the  same  igneous  agency  as  vol- 
canoes and  earthquakes. 

Hot  springs  are  found  most  commonly  in  the  vicinity  of  volcanoes  ;  but 
they  also  occur  in  countries  which  at  present  afford  no  evidence  of  volcanic 

QUESTIONS. — What  circumstances  lead  to  the  opinion  that  earthquakes  and  volcanoes 
have  a  common  origin  ?  To  what  are  the  phenomena  of  thermal  springs  attributed  ? 
Where  do  hot  springs  occur  ? 


*  Mr.  Mallet,  of  England,  who  has  made  the  study  of  earthquakes  a  specialty,  and  who 
entirely  rejects  the  supposition  that  the  interior  of  the  earth  is  in  a  state  of  igneous  fluid- 
ity, after  noticing  the  circumstance,  that  the  magnetism  of  the  earth  is  in  some  way 
connected  with  the  phenomena  of  spots  upon  the  disc  of  the  sun,  says:  "We  find,  then, 
that  both  sun  and  moon  influence,  with  other  and  more  occult  forces  than  those  which 
address  sense  and  eye,  our  planet,  and  that  these  all  incessantly  modify  the  conditions 
and  relations  of  every  grain  of  matter  in  the  inmost  recesses  of  its  nucleus.  While  every 
cosmical  force  is  also  found  to  be  correlated  to  every  other,  all  mutually  convertible,  and 
capable  of  appearing  and  disappearing,  '  by  measure,  number,  and  weight,1  as  mere  brute 
power  or  mechanical  force,  it  is  not  too  much,  at  least,  to  affirm  the  advancing  probability 
that  a  distinctly  (though  irregularly)  periodic  phenomenon,  such  as  earthquakes,  will  be 
found  intimately  related  to  them,  possibly  with  no  very  long  or  intricate  intermediate 
chain  of  causation.11  A  similar  theory  has  also  been  recently  advocated  by  Dr.  C.  F. 
Winslow,  of  Boston,  Mass. 


IGNEOUS     AGENCIES.  119 

activity.  The  majority  of  them,  however,  riso  from  rocks  of  a  volcanic 
nature,  from  mountain,  chains,  or  from  points  of  disruption  in  strata.  But 
wherever  their  location,  it  requires  no  demonstration  to  prove  that  boiling 
water,  continually  issuing  from  the  earth,  must  come  from  a  depth  where 
boiling  heat  continually  exists.  It  is,  furthermore,  strong  evidence  of  the 
connection  between  hot  springs  and  volcanic  phenomena,  that  earthquakes 
and  volcanic  eruptions  are  known  to  have  affected  the  temperature  of  such 
springs.  Thus,  after  the  occurrence  of  an  earthquake  in  the  north  of  Spain, 
the  temperature  of  a  celebrated  hot  spring  in  the  Pyrenees,  was  so  much -re- 
duced as  to  be  no  longer  of  any  value.  In  the  year  of  the  great  earthquake 
at  Lisbon,  another  spring  among  the  Pyrenees  rose  75°  in  temperature. 

Hot  springs  are  of  all  degrees  of  temperature,  between  that  of  the  sur- 
rounding air  and  boiling  water.  They  (with  few  exceptions)  discharge  at 
all  times  the  same  quantity  of  water,  and  their  temperature  remains  con- 
stant. There  is  evidence  to  show  that  the  temperature  of  some  hot  springs 
has  not  diminished  during  the  last  thousand  years.  The  waters  of  thermal 
springs  are  frequently  so  charged  with  gases  and  mineral  substances  that 
they  are  termed  "mineral  waters;"  as,  for  example,  the  Sulphur  Springs  of 
Virginia,  of  Bath  in  England,  and  Baden  in  Germany. 

In  the  United  States  the  most  remarkable  hot  springs  occur  in  Virginia, 
Arkansas,  Oregon,  California,  and  Territory  of  Utah.  In  Arkansas,  upward 
of  seventy  have  been  enumerated,  which  range  in  temperature  from  118°  to 
148°  Fahrenheit. 

Those  of  the  Napa  Valley,  California,  discovered  in  1851,  are  thus  described 
by  Prof.  Forrest  Shepherd:  "Within  the  space  of  a  half  mile  square  are 
from  one  to  two  hundred  openings,  through  which  the  steam  issues  with 
violence,  sending  up  columns  of  dense  vapor  to  the  height  of  150  to  200  feet. 
The  roar  of  the  largest  of  these  can  be  heard  for  a  mile  or  more.  Many  of 
the  openings  work  spasmodically,  precisely  like  high-pressure  engines,  throw- 
ing out  occasional  jets  of  steam  or  volumes  of  hot,  scalding  water,  some 
twenty  or  thirty  feet  high,  endangering  the  lives  of  those  who  rashly  venture 
too  near.  Numerous  cones  are  formed  by  the  accumulation  of  various  mineral 
salts,  and  by  deposits  of  sulphur  crystals  with  eafthy  matter.  Frequently 
the  streams  of  boiling  water  mount  up  to  the  top  of  these  cones  with  violent 
ebullition,  giving  to  the  cones  an  appearance  of  being  immense  boiling  cal- 
drons." 

Of  all  hot  springs,  those  of  Iceland,  known  as  the  "Geysers"  (raging  foun- 
tains) are  the  most  celebrated.  They  occur  in  a  group  of  one  hundred  or 
more,  in  the  vicinity  of  Mt.  Hecla,  The  largest,  termed  the  "Great Geyser," 
consists  of  a  nearly  circular  basin,  fifty  feet  in  diameter,  and  about  four  feet 
deep.  In  the  center  is  a  well  or  tube,  eight  or  ten  feet  in  diameter,  and 
seventy-five  feet  in  perpendicular  depth.  Through  this  tube  hot  water,  hold- 

QTTESTIONS. — Is  there  any  evidence  that  hot  springs  are  connected  with  the  agencies 
that  occasion  volcanoes  and  earthquakes  ?  Are  hot  springs  found  in  the  territories  of  th« 
United  States'?  Enumerate  some  of  them  ?  What  are  the  most  celebrated  examples  of 
hot  springs  ? 


120          FIRST     PRINCIPLES     OF     GECKLOGY. 

FIG.  73. 


ing  silica  in  solution,  is  continually  bubbling  over  into  the  basin,  depositing 
silicious  sinter  at  the  bottom  and  round  the  cavity.  When  tho  basin  is  full, 
subterranean  explosions,  like  the  firing  of  distant  cannon,  are  heard  at  inter- 
vals of  some  hours,  accompanied  with  a  tremulous  motion  of  the  ground. 
-Louder  explosions  succeed ;  tho  water  becomes  agitated ;  steam  escapes  in 
large  quantities,  and,  finally,  a  column  of  boiling  water  is  thrown  up  with 

QtrrsTiox.— Describe  the  action  of  the  Geysers. 


IGNEOUS     AGENCIES.  121 

great  violence  to  the  height  of  one  or  two  hundred  feet.  After  the  water 
ceases  to  play,  a  column  of  steam,  rushing  up  with  amazing  force  and  deaf- 
ening explosion,  terminates  the  eruption.  Fig.  73  represents  the  Great 
Geyser  of  Iceland  in  action. 

130.  Modifications   of  the   Earth's   Surface   produced 
through   Igneous   Agencies, — Earthquakes   and  volcanoes 
are   powerful   agents  in  producing   modifications  of  the 
earth's  surface. 

During  the  earthquake  in  Chili,  in  1822,  the  coast  of  South  America,  for 
upward  of  a  hundred  miles,  was  elevated  from  two  to  seven  feet ;  while  the 
whole  area  of  territory  permanently  uplifted  at  the  same  time,  was  estimated 
at  100,000  square  miles — an  extent  of  country  equal  to  one  half  the  area  of 
France,  or  about  five-sixths  of  the  area  of  the  whole  of  Great  Britain.* 

In  1819,  during  an  earthquake,  near  the  mouth  of  the  Indus,  a  tract  of 
land,  2,000  square  miles  in  area,  was  permanently  depressed  and  converted 
into  an  inland  sea ;  while  another  portion  of  country,  fifty  miles  in  length 
and  several  miles  in  width,  was  elevated  at  the  same  time  to  a  nearly  uni- 
form height  of  ten  feet.  In  1692  the  harbor  and  part  of  the  town  of  Port 
Eoyal,  in  Jamaica,  suddenly  sunk,  during  an  earthquake,  to  a  depth  of  nearly 
fifty  feet.  Numerous  other  examples  of  a  lik"e  character,  occurring  within 
the  historic  period,  might  also  be  cited. 

131.  Gradual    Elevations    and    Depressions, — Another 
apparent  manifestation  of  subterranean  igneous  agency  is 
the  gradual  elevation   or  depression  of  portions  of  the 
earth's  surface. 

One  of  the  most  interesting  local  examples  of  this  action  is  afforded  by  the 
remains  of  the  temple  of  Jupiter  Serapis,  which  was  built  on  the  shore  of  the 
Mediterranean,  near  Naples,  about  eighteen  hundred  years  ago.  Its  ruins 
remained  unnoticed  until  1849,  at  which  time  three  columns  were  discovered 
projecting  a  little  above  the  surface  of  the  ground,  which,  when  excavated, 
were  found  to  be  composed  of  single  blocks  of  marble  forty  feet  high,  resting 
upon  a  pavement  or  platform.  (See  Fig.  74.)  The  surfaces  of  these  columns 
are  smooth  and  uninjured,  to  an  elevation  of  about  twelve  feet  from  the 
pedestal,  where  a  band  of  perforations,  made  by  a  species  of  marine  boring 
shell  (Litliodomos\  inhabiting  the  Mediterranean,  commences  and  extends 

QUESTIONS. — What  influence  have  earthquakes  and  volcanoes  in  modifying  the  earth's 
surface?  Give  some  examples.  Do  elevations  and  depressions  of  the  earth's  surface 
take  place  gradually  ?  What  is  a  remarkable  local  example  ? 

*  "  If  we  suppose  the  elevation  to  have  been  only  three  feet  on  an  average  over  this 
extent  of  territory,  the  mass  of  rock  added  to  the  continent  of  America  by  this  earth- 
quake, or,  in  other  words,  the  mass  of  rock  previously  below  the  level  of  the  sea,  and 
afterward  permanently  above  it,  must  have  been  equal  to  fifty-seven  cubic  miles  in  bulk, 
which  would  be  sufficient  to  form  a  conical  mountain  two  miles  high,  with  a  circumfer- 
ence at  the  base  of  nearly  thirty-three  miles.'1—  Lyell. 

6 


122        FIRST     PRINCIPLES     OF     GEOLOGY 


to  the  height  of  nine  feet,  above  which  all  traces  of  their  ravages  disappear. 
These  perforations,  many  of  which  still  contain  shells,  are  so  numerous  and 


FIG.  74. 


deep  as  to  render  it  certain  that  the 
pillars  were  immersed  in  sea  water 
at  a  time  when  their  base  and  lower 
portions  were  protected  by  rubbish 
and  sediment,  and  that  the  upper 
portions  at  the  same  time  projected 
above  the  water,  and  were,  conse- 
quently, placed  beyond  the  reach 
of  the  lithodomi.  The  platform  of 
the  temple  is  now  about  one  foot 
below  high  water  mark,  and  the 
sea  is  120  feet  distant  The  evi- 
dence, therefore,  is  conclusive  that 
the  columns  were  first  depressed, 
and  after  remaining  partially  sub- 
merged in  the  sea  for  a  consider- 
able period  were  again  elevated; 
thus  incontestably  proving  that  the 
relative  level  of  land  and  sea  in 
that  part  of  the  Mediterranean  coast 
has  changed  more  than  once  during 
the  Christian  era;  and  that  each 
movement  of  siibsidence  and  elevation,  exceeding  twenty  feet,  took  place 
so  gradually  that  the  columns  continued  to  maintain  their  upright  position. 
At  the  present  time  the  columns  appear  to  be  again  subsiding,  and  a  change 
in  their  position  lias  been  recognized  within  the  last  few  years.  The  coun- 
try in  their  immediate  vicinity  exhibits  marked  evidence  of  volcanic  activity. 

A  gradual  change  in  the  relative  level  of  land  and  sea 
has  also  been  noticed  on  an  extensive  scale  in  regions  not 
subject  to  the  action  of  volcanoes  and  earthquakes. 

Thus,  in  Sweden,  for  example,  a  line  traverses  the  southern  part  of  that 
kingdom  from  the  Baltic  to  the  Cattegat,  to  the  north  of  which,  even  as  far 
as  the  North  Cape  of  Europe,  there  is  evidence  scarcely  disputable  that  the 
land  is  gradually  rising  at  the  average  rate  of  nearly  four  feet  in  a  century ; 
while,  to  the  south  of  this  line,  there  are  similar  proofs  of  a  slow  subsidence"'. 

QUESTION.— What  is  said  of  the  elevation  and  depression  of  land  now  going  on  in 
Sweden? 

*  The  gradual  elevation  of  the  northern  portions  of  Sweden  and  Norway  is  proved  by 
observations  of  marks  cut  in  the  rocks  along  the  sea-coast;  and  also  by  the  fact  that 
numerous  beds  of  shells,  of  the  same  species  as  those  now  inhabiting  the  Baltic,  together 
with  rocks  covered  with  barnacles,  are  found  at  elevations  of  from  100  to  600  feet  abova 
ths  present  sea-level.  The  subsidence  of  the  coast  of  southern  Sweden  is  also  indicated 
by  the  circumstance  that  the  streets  of  ancient  seaport  towns  are  now,  in  some  instances, 
covered  with  water ;  and  also  by  the  record  of  measurements  made  during  the  last  century. 


IGNEOUS     AGENCIES.  123 

On  the  other  hand,  the  entire  western  coast  of  Greenland  has,  for  tho  last 
two  centuries,  been  gradually  sinking,  and  tho  locations  of  the  early  European 
settlements  are  now  entirely  or  in  part  submerged. 

Evidence  has  also  been  collected,  showing,  beyond  all  question,  that  the 
eastern  coast  of  South  America,  from  the  Rio  de  la  Plata  to  the  Straits  of  Ma- 
gellan, a  distance  of  1,200  miles,  has  been  raised  in  the  most  quiet  manner, 
and  within  a  comparatively  recent  period,  to  an  elevation  of  from  100  to 
140  feet  in  height;  and  that  over  wide  areas  of  the  Pacific  and  Indian 
oceans  a  part  of  the  islands  are  at  present  rising  while  others  are  slowly 
subsiding. 

Evidences  of  similar  changes  may  also  be  observed  in 
various  parts  of  the  United  States. 

At  Lubec,  on  the  northern  coast  ""  Maine,  barnacles  (a  species  of  marine 
shell)  are  found  attached  to  rocks  which  are  at  present  eighteen  feet  above 
high  water.  Beds  of  clay,  sand,  and  gravel,  containing  numerous  speaies  of 
shells,  now  living  upon  tho  Atlantic  coast,  and  presenting  other  evidence  of 
being  ancient  sea-bottoms,  are  found  in  many  localities  in  our  country  at 
heights  varying  from  fifty  to  nearly  GOO  feet  above  the  present  sea-level:  as 
at  Montreal,  540  feet  high  ;  in  the  valley  of" Lake  Champlain,  400  feet;  and 
near  Quebec,  200  feet. 

The  evidence  of  subsidence  in  other  localities  is  almost  equally  striking. 
Thus,  most  persons  at  all  familiar  with  shore  life,  must  have  observed  at 
different  points  on  the  Atlantic  coast  the  remains  of  logs,  stumps,  and  roots 
submerged  below  the  present  tide  level.  These  are  generally  regarded  as 
the  remains  of  trees,  torn  from  their  original  places  of  growth  by  currents  or 
by  the  wearing  away  of  the  shores,  and  deposited  where  they  are  found  by 
the  ordinary  action  of  water.  To  any  one  who  examines  them  carefully, 
however,  it  soon  becomes  evident  that  they  grew  upon  the  spots  where  they 
now  are ;  inasmuch  as  their  stumps  remain  upright,  their  roots  aro  still  fast 
in  the  earth,  and  in  many  caps  the  bark  and  small  roots  are  still  adherent. 
In  protected  situations  upon  tho  low,  sloping  shores  of  New  Jersey  and 
Long  Island,  areas  embracing  thousands  of  acres  can  be  found,  in  which  the 
bottoms  of  bays  and  marshes  are  as  thickly  set  with  the  stumps  of  trees  as 
the  ground  of  any  living  forest.  It  is  also  stated  by  Dr.  Emmons,  Superin- 
tendent of  the  Geological  Survey  of  North  Carolina,  that  tho  bottoms  of  the 
sounds  on  that  coast  are  everywhere  so  thickly  studded  with  stumps  of  the 
common  pine  of  the  mainland,  that  it  is  necessary  to  remove  them  by  gun- 
powder before  a  net  can  be  drawn  for  fishing. 

These  and  a  multitude  of  other  similar  facts  render  it  certain,  that  large 
portions  of  the  solid  crust  of  tho  globe,  whether  land  or  sea-bottom,  are  in  a 
state  of  constant  fluctuation  as  regards  level.  To  such  movements  as  these, 

QUESTIONS.— What  of  the  depression  of  Greenland?  What  of  fluctuations  of  the  earth's 
crust  in  South  America  and  the  Pacific?  What  evidence  is  there  that  similar  changes 
have  ocsurred  in  the  United  States  ?  What  is  said  of  the  existence  of  submarine  forests 
on  the  Atlantic  coast?  What  inference  may  we  draw  from  these  examples? 


124        FIRST     PRINCIPLES     OF     GEOLOGY. 

moreover,  acting  in.  times  past,  geologists  ascribe  the  elevation  of  the  whole 
of  the  present  land-surface  of  the  globe  above  the  waters  of  the  ocean.  We 
say  the  whole  of  our  present  land-surface,  because  by  far  the  greater  portion 
of  the  dry  land  is  now  covered  by,  or  made  up  of,  rocks  which  must  have 
been  formed  and  consolidated  on  the  bottom  of  the  ocean ;  and  of  the  re- 
mainder, where  igneous  rocks  now  prevail  at  the  surface,  we  have  every  rea- 
son to  believe  that  the  greater  part  at  least,  if  not  the  whole,  was  once 
covered  by  rocks  of  aqueous  origin. 

To  such  gradually  actir%  forces  we  must  ascribe  not  merely  the  elevation 
of  all  land,  but  also  those  diversities  of  the  earth's  surface  which  have  resulted 
from  unequal  elevation,  such  as  mountain-ranges,  table-lands,  valleys,  and 
the  depressions  of  the  ocean,  with  many  of  the  disturbances,  fractures,  and 
contortions  of  rock  strata,  which  have  been  already  noticed.* 

Nor  is  the  configuration  and  extent  of  the  terrestrial  surface  alone  affected 
by  such  movements ;  inasmuch  as  the  generic  distribution  of  animals  and 
plants  is  governed  in  a  great  measure  by  altitude  above  the  sea ;  and  one 
may  readily  perceive,  therefore,  how  gradual  elevations  of  the  land  must 
also  gradually  change  the  character  and  distribution  of  the  life  upon  its  sur- 
face. As  the  sea-bottom,  moreover,  will  also  partake  of  the  same  fluctuations 
as  the  land,  marine  life,  which  is  known  to  be  more  sensitive  to  physical 
changes  than  terrestrial,  must  also  be  sensibly  influenced.  Recent  scientific 
investigations  have  shown  that  the  sea-bottom,  from  the  shore  daily  covered 
by  the  tides  to  the  greatest  depths  to  which  life  and  organization  extend,  is 
divided  into  zones,  each  of  which  is  characterized  by  its  own  peculiar  sea- 
weed or  shell-fish  ;  and  any  derangement  of  these  zones,  therefore,  whether 
sudden  or  gradual,  must  necessarily  bo  followed  by  changes  in  their  types  of 
animal  and  vegetable  life,  and  possibly  by  the  extinction  of  whole  races  or 
families. 

As  to  the  cause  of  such  fluctuation  in  the  crust  of  the  earth,  geologists 
have  not  been  able  to  furnish  any  entirely  satisfactory  explanation.  Earth- 
quakes have,  in  some  instances,  affected  the  level  of  limited  districts ;  but 
this  agency,  when  applied  to  the  elevation  of  whole  continents,  seems  alto- 
gether inadequate.  The  theory  most  generally  favored  is,  that  an  explanation 
of  the  phenomenon  in  question  is  to  be  found  in  fluctuations  of  temperature 
in  the  heated  interior  of  the  earth.  Thus,  great  accessions  of  heat,  rising 


QTTESTTOXS. — What  has  probably  been  the  condition  of  the  greater  portion  of  the  earth's 
surface  during  some  former  period  ?  What  effect  have  gradual  uprisings  had  upon  the 
configuration  of  the  earth's  surface  ?  What  effect  have  such  movements  upon  animal 
and  vegetable  life  upon  the  earth?  What  has  been  ascertained  in  regard  to  the  distri- 
bution of  marine  life  ?  What  causes  have  been  assigned  for  fluctuations  of  the  earth's 
crust? 


*  The  existence,  in  almost  all  quarters  of  the  globe,  of  ancient  eea-beaches,  or  coast- 
lines, at  elevations  varying  from  ten  to  several  hundred  feet  above  the  present  sea-level, 
affords  us  some  indications  of  the  extent  of  the  changes  which  have  been  produced  in 
the  appearance  and  condition  of  the  earth's  surface  by  elevations  within  a  comparatively 
recent  period. 


IGNEOUS     AGENCIES.  125 

nearer  the  surface  in  one  part  than  another,  would  cause  expansion  of  the 
rocks  affected  by  it  in  every  direction,  and  produce  an  outward  bulging  or 
elevation  of  the  rocks,  accompanied,  it  may  be,  by  injection  of  molten  matter 
among  them :  while,  on  the  other  hand,  local  refrigeration  would  tend  to 
produce  shrinkage  and  contraction  of  the  rocks,  and,  consequently,  depression. 
Experiments  made  some  years  since,  by  officers  of  the  Topographical  Corps 
of  U.  S.  Engineers,  on  the  expansion  of  various  rocks  by  heat,  furnished 
data  which  proved,  that  if  a  mass  of  sandstone,  a  mile  in  thickness,  should 
have  its  temperature  raised  200°  F.,  it  would  expand  sufficiently  to  lift  almost 
any  amount  of  super-imposed  rock  ten  feet  above  its  former  level.  It  would 
also  appear  that  if  a  part  of  the  earth's  crust,  100  miles  in  thickness,  and 
equally  expansible,  were  to  have  its  temperature  raised  G00°  or  800°,  it 
would  probably  produce  an  elevation  of  between  two  and  three  thousand 
feet,  while  the  cooling  of  tho  same  mass,  subsequently,  might  cause  the  up- 
lifted material  to  sink  down  again  and  resume  its  original  position.  In  such 
an  agency,  therefore,  we  can  find  a  plausible  explanation  of  the  gradual  rise 
of  land  in  Sweden,  or  South  America,  or  the  subsidence  of  Greenland,  or  of 
the  bottom  of  the  Pacific  Ocean. 

132.  Speculations    concerning    the   Original   Condition 
and  Formation  of  onr  Globe, — The  theory  of  central  heat, 
so  generally  adopted,  extends  no  further  back  than  the 
time  when  the  ivliole  globe  was  assumed  to  be  in  a  state 
of.  complete  fusion  and  incandescence.     The  mind,  how- 
ever, not  willingly  accepting  any  limit  to  its  speculations, 
naturally  seeks  to  know  the  origin  of  this  vast  accumula- 
tion of  heat,  or  what  was  the  condition  of  the  matter  con- 
stituting our  planet  at  the  commencement.    In  prosecuting 
the  inquiry,  the  geologist  finds  little  to  assist  him  in  the 
truths  which  belong  especially  to  his  own  science,  but  must 
enter  into  the  departments  of  astronomy  and  chemistry. 

133.  Nebular  Hypothesis, — Modern  science  presents  us  with  only 
one  hypothesis  which  in  a  consistent  and  satisfactory  manner  attempts  to 
reveal  to  us  the  condition  of  matter  in  what  may  be  called  the  beginning. 
The  outlines  of  this  theory,  and  the  evidence  upon  which  it  is  based,  may  be 
briefly  stated  as  follows : 

Our  solar  system,"  of  which  the  earth  is  a  member,  viewed  superficially, 
presents  to  us  the  idea  of  a  vast  luminous  body — the  sun,  occupying  a  central 
position,  with  a  number  of  smaller,  though  various-sized  bodies  revolving  at 

QUESTIONS. — What  experiments  have  been  made  on  the  expansion  of  rocks  by  heat? 
To  what  extent  does  the  theory  of  central  heat  extend  ?  Does  geology  furnish  in  itself 
any  evidence  of  the  earliest  condition  of  matter  ? 


126       FIRST     PRINCIPLES     OF     GEOLOGY. 

different  distances  about  it;  some  of  which,  in  turn,  have  smaller  planets  or 
satellites  revolving  about  them.  A  closer  examination,  however,  makes  us 
acquainted  with  some  very  singular  peculiarities  in  the  structure  of  this  so- 
called  "solar  system."  Thus,  in  the  first  place,  it  is  a  very  singular  fact  that 
the  orbits  of  the  planets  are  all  nearly  circular,  and  that  their  planes  are 
nearly  coincident  with  (or  in  the  same  line  with)  the  plane  of  the  sun's  equa- 
tor. 

Next,  it  is  not  less  remarkable  that  the  motions  of  the  planets  around  the 
sun,  and  the  satellites  around  the  planets,  and  finally,  that  the  motions  of  all — 
sun,  planets,  and  satellites — around  their  axes,  should  be  only  in  one  direc- 
tion, viz.,  from  west  to  east ;  that  the  periods  of  revolution  grow  shorter  in 
the  planets  and  •  satellites  as  their  distances  from  their  primary  grow  less : 
that  the  sun  rotates  on  its  axis  in  a  shorter  period  than  that  employed  in  the 
revolution  of  any  planet ;  and  that  every  planet,  accompanied  by  satellites, 
rotates  on  its  axis  in  a  less  time  than  the  period  of  revolution  of  any  satellite. 
These  peculiarities  suggested  to  Laplace — the  eminent  French  astronomer  arid 
mathematician — the  idea  that  all  the  matter  of  the  solar  system  was  once  a 
connected  mass,  endowed  with  a  uniform  motion  in  one  direction.  He  fur- 
ther showed,  that  while  this  hypothesis  and  its  deductions  explained  fully 
the  peculiarities  noticed,  they  were  not  accounted  for  by  any  other  supposi- 
tion; and  also,  that  had  the  existing  arrangement  of  the  solar  system  been 
left  to  accident,  the  chances  against  the  occurrence  of  the  present  organiza- 
tion would  have  been  as  four  millions  of  millions  to  one. 

Coincident  with  these  investigations  was  the  discovery,  by  astronomers,  of 
the  existence,  in  space,  far  removed  from  our  system,  of  an  immense  number 
of  objects,  which,  from  their  foggy,  cloudy  appearance  have  been  called 
nebulae : — some  of  vast  extent  and  irregular  outline,  as  that  in  the  Sword  of 
Orion,  which  is  visible  to  the  naked  eye ;  others  of  shape  more  denned  and 
regular;  and  others  again  in  which  small,  bright  nuclei,  apparently  con- 
densed points,  appear  here  and  there  over  the  surface.  Ascending  higher 
as  it  were  in  the  scale  of  progress,  we  have  next  clusters  of  nuclei,  with 
nebulous  matter  around  them;  and  then  what  are  called  "nebulous  stars," 
or  luminous  spherical  objects — bright  in  the  center  and  dull  toward  the 
extremities — existing,  however,  in  every  stage  of  concentration,  from  stars 
with  ill-defined  centers,  to  stars  invested  with  pnly  a  slight  burr  or  hazi- 
ness. The  figures  in  plate  75  represent  some  of  these  various  forms  of 
nebulae,  as  seen  through  a  telescope. 

Upon  these  facts,  mainly,  has  been  built  up  the  so-called  "  nebular  hypothe- 
sis,11 which  supposes  that  the  various  appearances  we  have  described,  represent 
the  various  conditions  which  suns,  systems,  and  worlds  pass  through  in  their 
progress  of  formation  ;  the  cloudy  nebulas,  representing  matter  in  its  original 
chaotic  condition ;  the  defined  nebuke,  the  first  stage  of  condensation ;  and 
nucleated  nebulas,  and  the  succession  of  nucleated  stars,  the  more  advanced 

QUESTIONS. — Viewed  superficially,  what  peculiarities  are  found  in  the  structure  of  the 
solar  system  ?  What  idea  was  suggested  to  Laplace  by  these  peculiarities  ?  What  prob- 
ability is  there  that  they  could  have  originated  through  accident  ? 


IGNEOUS     AGENCIES. 


127 


and  final  stages ;— just  as  a  child,  a  boy,  a  youth,  a  middle-aged,  and  an  old 
man,  indicate  the  successive  periods  in  the  life  of  a  human  being.* 

Bat  whatever  may  bo  the  physical  condition  of  the  nebulae,  the  main  fea- 
tures of  the  theory  of  Laplace  curiously  accord  with  the  antecedent  condition 
of  our  system  as  deduced  from  its  present  peculiarities ;  and  it  is  accordingly 

FIG.  75. 


inferred  that,  in  the  "beginning,"  our  solar  system  was  an  immense  sphere 
of  nebulous  matter,  filling  all  tho  space  now  occupied  by  the  system*  and  ex- 
tending even  to  a  point  far  beyond  the  limits  of  the  orbit  of  Neptune — a 
planet  whose  average  distance  from  the  sun  is  about  three  billions  of  miles,  f 


QUESTIONS.— What  are  the  nebulae?  What  is  the  hypothesis  called  that  attempts  an 
explanation  of  their  appearances  ?  What  does  this  hypothesis  assume  was  the  former 
state  of  the  solar  system  ? 


*  It  has  heen  urged  of  late  that  the  resolution  of  many  of  the  nebulae,  under  the  power- 
ful  telescope  of  Lord  Rosse,  into  stars,  or,  in  other  words,  the  proving  that  the  misty 
condition  of  some  of  these  bodies  was  due  to  distance  rather  than  condition,  was  fatal  to 
the  assumptions  of  this  theory  ;  but  this  opinion  is  not  generally  entertained  by  astrono- 
mers, and  the  best  authorities  are  now  agreed,  that  even  if  all  the  nebulae  were  resolved 
(which,  as  yet,  is  very  far  from  being  the  case)  the  remaining  evidence  in  favor  of  the  hy- 
pothesis is  almost  incontrovertible. 

t  Astronomers,  knowing  the  present  mass  and  weight  of  the  sun,  planets,  and  satellites, 
have  even  been  able  to  calculate  the  extent  of  expansion  to  which  their  material  particles 
must  have  been  subjected  in  order  to  fill  up,  uniformly,  this  enormous  space,  and  it  has 


128        FIRST     PRINCIPLES     OF     GEOLOGY. 

Assuming  the  existence  of  such  a  nebula  in  the  first  instance,  the  general 
attractive  force  resident  in  all  matter  would  gradually  cause  its  particles  to 
approach  each  other,  and  thus,  from  the  outset,  the  nebulous  sphere  must 
have  commenced  condensing  and  contracting.  "It  is,  moreover,  a  well-known 
law  of  physics,  that  when  fluid  matter  (gaseous  or  liquid)  collects  toward,  or 
meets  in  a  center,  it  establishes  rotary  motion.  Every-day  illustrations  of 
this  law  may  be  seen  in  the  whirlpool  or  whirlwind,  or,  to  use  a  more  hum- 
ble illustration,  in  water  sinking  through  the  aperture  of  a  funnel.  Thus, 
rotation  on  an  axis  would  commence,  at  first  slow,  but  become  quicker 
and  quicker  as  the  condensation  increased."  "With  the  establishment  of  rotary 
motion,  a  tendency  in  the  mass  to  throw  off  its  outer  portions  would  bo  gene- 
rated, in  consequence  of  the  centrifugal  force  overpowering  the  central  attrac- 
tion ;  and  it  is  accordingly  supposed  that  masses  of  matter  were,  in  fact,  from 
tune  to  time,  torn  away  from  the  nebulous  sphere,  which  detached  portions 
afterward  continued  their  courses  separate  from  the  main  mass,  but  pi'eserv- 
ing  a  similar  direction  in  their  motion.  Such  detached  masses,  abandoned 
successively  at  different  stages  of  the  condensation,  formed  themselves  into 
single  planets,  or  like  to  the  great  original  sphere,  into  planets  with  satel- 
lites and  rings,  until,  finally,  the  principal  mass  condensed  itself  into  the  sun, 
which  still  occupies  its  original  position  as  the  center  of  the  system,  and  as 
the  largest  body. 

Simultaneously  with  the  commencement  of  condensation  in  the  nebulous 
matter,  the  force  heat  must  have  manifested  itself)  since  it  is  a  general 
law  in  physics  that  the  condensation  or  compression  of  ali  matter,  under  all 
circumstances,  evolves  heat ;  and  as  condensation  and  refrigeration  further 
progressed,  by  the  radiation  of  heat  into  space,  other  forces — as  chemical 
affinity,  cohesion,  etc., — must  have  exerted  an  influence,  until,  at  last,  the 
constituent  materials  of  our  earth  and  the  other  planetary  bodies,  passed 
from  a  gaseous  to  a  fluid  or  solid  condition,  and  assumed  their  present  forms 
and  properties. 

134.  §uch  is  a  general  outline  of  the  only  consistent  and  plausible  theory 
by  which  modern  science  attempts  to  trace  back  the  history  of  the  formation 
of  our  earth,  the  sun,  and  its  associate  planets.  It  may  also  be  remarked, 
that  the  suppositions  of  science  involved  in  the  nebular  hypothesis  are  not 
antagonistic  to  the  Mosaic  account  of  creation.  This  will  appear  evident,  if 
we  remember  that  that  which  Moses  names  heaven  is  different  from  the  blue 

QUESTIONS.— Assuming  the  existence  of  such  a  nehula,  what  changes  would  probably 
take  place  in  it  ?  In  what  manner  was  the  solar  system  supposed  to  have  been  formed  ? 
"What  development  of  force  must"have  accompanied  condensation  ?  Is  the  nebular  theory 
antagonistic  to  the  Mosaic  accounts  of  creation  ? 


been  found  that  the  density  of  this  hypothetical  nebula  must  have  been  so  small  that  all 
the  matter  included  within  three  cubic  miles  would  have  weighed  less  than  a  single  grain. 
Incredible  as  this  statement  may  seem,  there  is  some  evidence  tending  to  show  that  the 
matter  constituting  -some  comets  exists  in  an  equal  state  of  tenuity. — See  Sabinefa  Re- 
searches on  the  Density  and  Mass  of  Comets ;— Annual  of  Scientific  Discovery  for  1858, 
pp.  361-864. 


IGNEOUS     AGENCIES.  129 

dome  above  us,  and  is  synonymous  with  space;  that  the  unformed  earth  was 
in  a  state  of  chaos  and  darkness,  and  that  the  separation  of  the  waters  of  the 
great  deep — which  were  afterward  divided  into  waters  above  the  firmament 
and  waters  below  the  firmament — resembles  the  process  of  condensation  and 
consolidation  by  which  the  chaotic  elements  of  the  earth  assumed  form  and 
arrangement. 

The  acceptance  of  this  theory,  moreover,  can  in  no  wise  affect  the  inference 
that  the  universe  is  the  work  of  a  wise  and  omnipotent  Creator.  "  Let  it  be 
assumed,"  says  Dr.  "Whewell,  "that  the  point  to  which  it  leads  us  is  the 
ultimate  boundary  of  physical  science;  that  the  furthest  glimpse  we  can 
obtain  of  the  material  universe  shows  it  to  be  occupied  by  a  boundless 
abyss  of  attenuated,  self-luminous  matter  (i.  e.,  the  nebulas);  still  we  are  left 
to  inquire  how  space  came  to  be  thus  occupied ;  and  how  matter  came  to  be 
thus  luminous ;  and  if  we  establish,  by  physical  proofs,  that  the  first  fact 
which  we  trace  in  the  history  of  the  universe  is,  'that  there  was  light,'  we 
shall  still  be  led,  even  by  our  natural  reason,  to  suppose  that  before  this  could 
occur  '  God  said,  Let  there  be  light.'  " 

In  addition  to  the  support  which  the  nebular  hypothesis 
derives  from  the  structural  peculiarities  of  the  solar  sys- 
tem, and  from  the  apparent  condition  of  the  nebulous 
bodies  existing  in  space,  various  other  facts  strongly  con- 
tribute to  render  its  suppositions  probable. 

Thus,  the  substance  of  comets  appears  to  be  a  kind  of  luminous  matter, 
attenuated  to  a  degree  almost  beyond  conception — matter,  possibly,  in  the 
condition  of  uncondensed  nebulas.  According  to  M.  Babinet's  observations 
on  the  comet  of  Encke,  and  that  of  1825,  the  densitv  of  the  substance  of  these 
bodies  could  not  be  calculated  at  so  high  a  quantity  as  that  of  our  atmos- 
phere, diminished  by  the  enormous  divisor,  forty-five  millions  of  billions.  "We 
may,  therefore,  regard  it  as  certain,  that  bodies  of  a  nebulous  character  still 
form  a  part  of  the  solar  system. 

Again,  it  is  found  that  the  planets  comprising  the  solar  system  exhibit 
gradations  of  density,  those  nearest  the  sun  (which,  by  the  nebular  hypothesis, 
must  have  been  thrown  off  last,  and  after  the  process  of  condensation  had 
long  continued)  being  much  denser  than  those  which  are  more  distant ;  thus, 
Mercury,  which  is  the  nearest  to  the  sun,  the  center,  is  the  heaviest,  being 
almost  thrice  as  dense  as  the  earth ;  while  the  density  of  Jupiter,  which  is 
far  removed,  is  not  more  than  one-third  that  of  our  planet;  and  Saturn, 
which  is  still  more  remote,  is  but  little  more  than  one-eighth  as  dense,  or 
about  as  light  as  cork. 

The  spheroidal  form  which  the  earth  now  presents  (see  §  5.,  p.  11) — en- 

QCEBTIONS. — Have  we  any  evidence  that  matter  analogous  to  the  nebulae  still  forma 
part  of  the  solar  system?  Does  the  density  of  the  several  planets  accord  with  the 
nebular  hypothesis? 

6* 


130       FIRST     PRINCIPLES     OF     GEOLOGY. 

largcd  at  the  equator  and  flattened  at  the  poles — is  also  precisely  that  which 
would  necessarily  arise  from  the  rotation  of  a  globular  mass  of  yielding  ma- 
terials on  its  own  axis.  The  same  peculiarity  of  structure,  moreover,  is 
found  in  all  the  other  planets;  and  in  the  planet  Jupiter  is  especially  mani- 
fest— its  equatorial  diameter  exceeding  the  polar  by  more  than  six  thousand 
miles.  But  if  tho  earth  and  the  other  planets  were  originally  fluid,  the  fluid- 
ity must  have  been  the  result  of  igneous  action ;  for  since  the  solid  matter  of 
the  globe  is  many  times  heavier  than  water,  the  solution  of  its  mineral 
constituents  in  such  a  solvent  would  be  impossible. 

135.  To  a  mind  unaccustomed  to  scientific  inquiry,  the  proposition  that 
our  planet  once  existed  in  a  gaseous  state  may  seem  somewhat  difficult  of 
conception;  but  this  difficulty  will  seem  less  formidable,  if  we  remember  that 
at  least  one-half  of  all  the  ponderable  matter  of  the  globe,  so  far  as  it  haa 
been  subjected  to  our  examination,  is  made  up  of  elements — oxygen,  hydro- 
gen, nitrogen,  etc.,  which  readily  assume,  or  may  be  said  to  exist  naturally, — 
in  a  gaseous  condition ;  while  the  remaining  more  solid  forms  of  matter  may 
all  be  vaporized  through  the  agency  of  heat. 

Furthermore,  the  transition  of  the  constituents  of  tho  earth,  according  to 
the  nebular  hypothesis,  from  a  state  of  gas  or  vapor  to  a  fluid  or  solid  con- 
dition, furnishes  in  itself  a  ready  explanation  of  the  origin  of  the  heat  which 
is  supposed  to  have  formerly  pervaded  the  whole  mass  of  our  planet,  and 
which  now  appears  to  exist  in  its  interior ;  inasmuch  as  a  degree  of  heat  suf- 
ficient to  meet  all  tho  requirements  o&  the  case  would  be  evolved  by  the  act 
of  condensation.  It  is  also  a  fact  worthy  of  note,  that  the  sun,  according  to 
tho  generally  received  theory,  is  even  now  in  a  state  of  igneous  fusion,  or  in 
such  a  condition  of  intense  heat  as  the  earth  is  supposed  to  have  been,  after 
condensing  from  a  gaseous  to  a  fluid  condition.* 

It  will  thus  be  seen  that  the  hypothesis  of  a  nebulous  origin  of  our  planet 
contains  within  itself  all  the  conditions  requisite  for  the  succeeding  changes 
to  which  it  appears  to  have  been  subjected;  it  being  considered  that  the 
globe  first  passed  from  a  gaseous  to  a  fluid  condition,  and  that,  subsequently, 
as  the  varied  processes  of  condensation,  refrigeration  (through  radiation  of 
heat),  and  rotation  proceeded,  a  thin  crust  cooled  and  solidified  upon  the 

QUESTIONS. — What  inference  lias  been  deduced  from  the  spheroidal  form  of  the  earth  ? 
Is  there  anything  in  the  constitution  of  terrestrial  matter  that  renders  its  existence  in  a 
gaseous  state  impossible  ?  Does  the  nebular  hypothesis  afford  any  explanation  of  the  in- 
ternal heat  of  the  earth.  What  is  the  theoretical  condition  of  the  sun  at  present?  As- 
suming the  nebulous  origin  of  our  planet,  what  have  been  the  succession  of  changes  to 
•which  it  has  been  subjected  ? 


*  According  to  Mr.  Helmholtz,  a  German  physicist,  it  has  been  calculated  that,  if  the  sun 
•were  diminished  by  condensation  to  the  extent  of  only  one  ten-thousandth  of  its  present 
diameter,  sufficient  heat  would  be  generated  by  the  act  to  compensate  for  the  total  emis- 
sion for  2,100  years.  But,  according  to  measurements  of  the  French  physicist,  Poullet, 
the  quantity  of  heat  emitted  from  the  entire  surface  of  the  sun,  per  hour,  is  equal  to  that 
which  a  layer  of  the  densest  coal,  ten  feet  thick,  extending  over  its  whole  surface,  would 
give  out  by  its  combustion. 


IGNEOUS      AGENCIES.  131 

molten  fluid  surface.*  As  the  temperature  of  the  exterior  still  further  dimin- 
ished, this  crust  thickened ;  the  existence  of  air  and  water  became  possible 
upon  it ;  contraction,  involving  both  subsidence  and  elevation  of  parts  of  the 
crust,  gave  configuration  to  the  surface  and  established  the  divisions  of  land 
and  water ;  and,  finally,  as  the  conditions  became  favorable,  the  first  forms 
of  animal  and  vegetable  life  were  called  into  existence  by  the  Creator,  and 
the  world  became  the  home  of  living,  organized  structures.  It  is  at  this 
point  that  geology,  leaving  the  domain  of  theory  and  speculation,  commences 
to  gather  facts  and  reliable  evidence  concerning  terrestrial  phenomena,  and 
becomes  entitled  to  rank,  in  a  measure,  with  the  exact  sciences ;  and  it  is 
from  this  point  also  that  the  history  and  chronology  of  the  stratified  or  aque- 
ous rocks  admit  of  determination. 

136.  Geology  of  other  Worlds, — As  has  been  already  stated,  the 
other  planets  and  satellites,  belonging  to  the  solar  system,  appear  to  have 
been  formed  by  the  same  agencies  as  the  earth.  There  is  also  good  reason 
to  believe  that  they  are  composed  of  essentially  the  same  materials.  Thus, 
the  masses  of  earthy  or  metallic  matter,  known  as  meteorites,  which  from 
time  to  time  fall  to  the  earth  through  the  atmosphere,  and  are  now  generally 
believed  to  have  been  derived  from  some  one  of  the  planetary  bodies,  con- 
tain no  elementary  substances  before  unknown  to  us,  although  the  conditions 
of  their  combination  are  somewhat  unusual,  f 

The  planets  which  most  nearly  resemble  our  earth  in  physical  condition 
are  probably  Venus  and  Mars.  Upon  the  surface  of  both  of  these,  mountain 
peaks  and  ranges  are  believed  to  exist ;  while  upon  the  surface  of  the  latter 
astronomers  have  fancied  they  could  recognize  the  presence  of  an  atmos- 
phere, as  well  as  the  existence  of  seas  and  the  outline  of  continents. 

Concerning  the  physical  condition  of  the  moon,  the  nearest  of  the  heavenly 
bodies,  we  have  more  definite  information,  and  as  the  result  of  telescopic  in^ 
vestigation  we  are  enabled  to  affirm,  with  almost  entire  certainty,  that  our 
satellite  has  been  the  theater  of  most  intense  volcanic  action.  Its  surface,  in 


QUESTIONS. — What  information  do  we  possess  respecting  the  geology  of  other,  worlds  ? 
What  planets  probably  most  resemble  our  earth  ? 


*  Assuming  that  the  earth  was  once  entirely  in  a  state  of  igneous  fluidity,  the  cooling 
and  solidification  of  its  exterior  must  have  been  exceedingly  gradua^  at  first,  and  still 
slower  after  the  formation  of  a  crust,  owing  to  the  slowness,  with  which  earthy  materials 
conduct  heat.  And  if  the  residuum  of  this  heat,  further-more,  now  pervades  the  central 
portions  of  the  earth,  it  has  most  probably  reached  a  fixed  point  in  temperature,  at  which 
it  will  remain  forever,  as  the  thickness  and  non-conducting  properties  of  the  present  crust 
would  seem  to  absolutely  prevent  its  diminution, 

t  Many  of  the  meteorites  which  fall  to  the  earth  from  the  interplanetary  spaces  have 
little  or  no  oxygen  in  their  composition,  and  in  this  respect  are  unlike  the  generality  of 
compound  substances,  which  make  up  the  crust  of  our  globe.  Hence,  the  inference  has 
been  drawn,  that  in  some  of  the  planetary  masses  of  the  solar  system,  from  whence 
meteorites  were  undoubtedly  derived,  oxygen  does  not  exist  at  all,  or  in  much  smaller 
proportions  than  upon  the  earth.  Many  meteorites  contain,  and  some  are  entirely  com- 
posed of,  metallic  iron  and  nickel ;  while  upon  the  earth  these  elements  are  rarely,  if 
ever,  found,  except  in  combination  with  other  substances. 


132      FIRST     PRINCIPLES     OF     GEOLOGY. 


fact,  is  like  that  which  we  may  conceive  would  be  presented  by  our  earth,  had 
its  exterior,  (since  it  cooled  and  consolidated)  remained  unaltered  by  the  action 
of  the  atmosphere,  water,  or  organic  life,  inasmuch  as  none  of  these  agencies 
are  probably  in  existence  upon  the  moon.  As  seen  with  a  powerful  telescope, 
the  surface  of  the  moon  exhibits  extensive  ranges  of  mountains  and  isolated 
peaks  of  extreme  steepness  and  distinctness  of  outline;  some  of  which  rise  to 
elevations  of  from  7,000  to  10,000  feet  above  the  general  level.  But  the 
most  remarkable  feature  of  the  lunar  scenery  is  the  existence  of  immense 
cup-shaped  cavities  or  depressions,  some  of  which  extend  beneath  the  gen- 

FIG.  76. 


eral  surface  to  a  depth  of  10,000  to  17,000  feet,  and  exceed  twenty  miles  in 
diameter.  " The  number  of  these  cavities,"  says  Prof. "Mitchell,  "is "beyond 
credibility;  and  in  case  we  admit  them  to  be  the  extinct  craters  of  once 
active  volcanoes,  we  are  forced  to  the  conclusion  that  convulsions,  such  as 
'the  earth  is  a  stranger  to,  have  shaken  the  outer  crust  of  our  satellite  into  a 
hideousness  of  form  unknown  in  any  region  of  our  planet.  That  these  con- 

QTTESTIO:*.— What  is  the  structure  of  the  moon  ? 


ATMOSPHERIC     AGENCIES.  133 

vulsions  are  of  different  ages  is  also  clearly  manifest,  from  the  fact  that  their 
outlines  very  often  overlap  one  another,  and  thus  the  oldest  and  newest  for- 
mations are  distinctly  traceable.  Very  often  the  interior  of  tfcese  cavities 
will  exhibit  a,  uniformly  shaded  surface,  and  in  the  center  a  conical  mountain 
will  lift  itself  far  above  this  level  plain.  So  sharp  and  positive,  moreover,  is 
the  outline  of  these  extraordinary  objects  that  we  cannot  but  feel,  that  some 
sudden  bursting  forth  might  even  occur  while  under  telescopic  examination." 
Fig.  76  represents  the  appearance  of  the  moon's  surface,  as  seen  through  a 
telescope,  during  the  second  quarter. 


SECTION     II. 

AQUEOUS      AND      ATMOSPHERIC      AGENCIES. 

137.  The  aqueous  and  atmospheric  agencies  most  prom- 
inently concerned  in  producing  geological  changes,  are 
rains,  and  the  gases  and  moisture  of  the  atmosphere, 
winds,  ice,  and  snow,  springs,  rivers,  ivaves,  tides,  and 
oceanic  currents. 

The  operation  of  water,  acting  mechanically,  is,  under  all  circumstances,  to 
wear  down  the  higher  portions  of  the  earth's  crust,  and  transport  the  materi- 
als to  lower  localities — an  action  which  obviously  tends  to  reduce  the  whole 
surface  to  a  smooth  and  uniform  level.  On  the  other  hand,  the  operations  of 
igneous  agents — volcanoes,  earthquakes,  eta — by  breaking  up  and  elevating 
the  crust  of  the  earth,  tend  to  counteract  the  equalizing  action  of  water 
and  to  produce  that  diversity  of  surface  which  is  indispensable  to  variety  in 
both  the  vegetable  and  animal  kingdoms.  These  two  forces,  therefore — the 
aqueous  and  the  igneous — may  be  considered  as  antagonistic  to  each  other, 
and  to  them  may  be  ascribed  the  principal  modifications  which  have  taken 
place,  and  are  still  taking  place,  in  the  crust  of  the  globe. 

138.  Rains,  and  the  Gases  and  Moisture  of  the  Atmos- 
phere • — "All  rain  falling  upon  land,  and  either  running  over  its  surface  or 
draining  through  its  interior,  is  constantly  abrading  and  carrying  off  particles 
of  pre-existing  rock,  in  the  shape  of  mud  and  sand.  From  the  gutters  and 
the  ditches,  from  the  rills,  the  streams,  and  the  brooks,  these  materials  for 
the  building  of  mechanically  formed  rocks  are  almost  unceasingly  carried 
into  the  rivers,  and  by  them  transported  to  the  beds  of  lakes  and  seas.  Rain, 
soaking  into  the  ground  and  issuing  as  springs  on  steep  slopes  or  precipices, 
sometimes  exerts  also  a  more  wholesale  destructive  power,  by  gradually 
loosening  and  undermining  very  considerable  masses  of  ground,  and  thus 

QUESTIONS, — What  are  the  prominent  aqueous  and  atmospheric  agencies  concerned  in 
producing  geological  changes  ?  What  are  the  relative  effects  of  igneous  and  aqueous 
action  ?  What  is  the  mechanical  effect  of  rains  on  the  earth's  surface  ? 


134       FIRST     PRINCIPLES     OF     GEOLOGY. 

causing  them  to  be  launched  forward  down  the  slope,  producing  what  are 
called  land-slips  or  slides." 

In  the  year  1806,  after  a  rainy  season,  a  mountain  in  Switzerland,  known 
as  the  Rossberg,  was  undermined,  and  a  mass  of  eighty  million  cubic  yards 
of  earth  and  rock  precipitated  into  the  adjacent  valley,  forming  hills  200 
feet  high,  and  burying  several  villages  with  their  inhabitants.  Some  remark- 
able land-slides  have  also  occurred  in  the  United  States.  In  1826,  one  near 
the  "Notch"  of  the  White  Mountains  destroyed  an  entire  family.  In  1836, 
a  mass  of  clay  and  earth,  estimated  to  weigh  200,000  tons,  slid  from  a  hill 
227  feet  high,  in  the  rear  of  the  city  of  Troy,  1ST.  Y.,  destroying  both  life  and 
property. 

The  fall  of  rain  varies  in  different  countries,  and  of 
course  will  be  attended  with  proportional  results.  In  the 
United  States  the  average  annual  fall  is  about  thirty- 
seven  inches  ;  while  in  tropical  countries  it  is  upward  of 
200  inches.  In  Guiana,  S.  A.,  twenty-one  inches  have 
been  known  to  fall  in  a  single  day.  Accustomed  to  the 
gentle  rains  of  our  own  latitude,  we  can  hardly  form  an 
estimate  of  the  changes  produced  by  such  sudden  and 
enormous  falls  on  the  surface-soil  and  river-courses  of  trop- 
ical countries. 

Water  also  effects  the  destruction  and  disintegration  of 
rocks  by  its  solvent  properties.  Pure  water  alone  dis- 
solves more  or  less  of  almost  every  variety  of  rock  ;  but 
when  the  water  contains  carbonic  acid  (as  it  generally 
does),  or  alkaline  substances,  its  solvent  action  is  much 
more  energetic. 

The  atmosphere,  partly  by  its  gases  and  partly  by  the 
moisture  always  diffused  through  it,  also  exerts  a  wasting 
or  weathering  in  all  rocks — softening,  loosening,  and  crum- 
bling down  their  constituent  particles,  to  be  more  readily 
borne  away  by  currents  of  wind  and  water. 

"  Carbonic  acid  acts  specially  on  all  rocks  containing  lime  ;  oxygen  rusts  or 
oxydizes  those  impregnated  with  iron ;  moisture  insinuates  itself  everywhere ; 
and  thus,  in  a  few  years,  the  hardest  rock  exhibits  a  weathered  or  wasted 
surface.  Particle  after  particle  is  loosened ;  film  after  film  falls  away ;  a  new 
surface  is  exposed  to  new  waste ;  and  in  the  course  of  ages  the  boldest 
mountain-mass  yields  to  the  silent,  imperceptible  agent." 

QTTESTIONS.— How  does  the  fall  of  rain  vary?  What  is  said  of  the  solvent  action  of 
water  ?  What  action  is  exerted  by  the  atmosphere  on  rocks  ? 


ATMOSPHERIC     AGENCIES.  135 

139.  Action  of  Winds.— Winds  occasionally  modify  the 
surface  of  the  earth  by  transporting  or  drifting  loose  ma- 
terials from  one  locality  and  accumulating  them  in  another. 
Such  accumulations  are  often  termed  sub-cerial,  in  contra- 
distinction to  those  formed  under  water,  and  hence  spoken 
of  as  aqueous  or  sub-aqueous. 

The  sandy  tracts,  so  frequent  along  our  sea  and  lake  shores,  and  known 
as  sand-drift,  or  sand-dunes  (dune  being  the  Saxon  word  for  a  mound), 
are  the  results  of  wind  agency — the  wind  carrying  the  dry  sand  left  by  the 
tides  forward  and  landward  beyond  the  reach  of  the  waters ;  while  the  land 
breezes  do  not  possess  sufficient  power  to  force  it  back.  In  this  way  hills  of 
drift  sand  are  formed,  which  sometimes  attain  an  elevation  of  200  or  300  feet. 
Such  hills  have  been  described  as  advancing  on  the  low  shores  of  France,  in 
the  Bay  of  Biscay,  at  the  rate  of  sixty  "and  seventy  feet  per  annum,  over- 
whelming fields,  forests,  and  villages  in  their  progress.  Similar  accumula- 
tions take  place  upon  the  shores  of  Cornwall,  in  England,  and  at  various 
points  on  the  coast  of  the  United  States,  especially  on  Cape  Cod  and  Nan- 
tucket,  where  the  interposition  of  the  National  Government  has  been  neces- 
sary to  prevent  the  threatened  destruction  of  harbors  and  villages. 

Nor  is  it  along  coasts  only  that  such  changes  are  taking  place.  In  the  in- 
terior of  great,  dry  continents,  there  are  vast  spaces  covered  with  sand  hills, 
which  are  shifted  and  carried  about  by  the  winds  in  the  same  manner  as 
sand-banks  are  removed  or  deposited  by  the  agency  of  water.  The  stories 
of  caravans,  being  overwhelmed  by  moving  columns  of  sand  on  the  African 
deserts  are  familiar,  as  is  also  the  fact  that  large  tracts  of  land  in  the  valley 
of  the  Nile,  which  in  the  days  of  the  Pharaohs  were  highly  fertile,  and  the 
sites  of  cities  and  temples,  are  now  buried  to  a  great  depth  by  the  accumu- 
lations of  sand  blown  in  from  the  Lybian  Desert 

140.  Action  of  Ice  and  Snow , — When  the  rain  or  mois- 
ture, which  penetrates  the  fissures  and  interstices  of  rocks, 
freezes,  its  conversion  into  ice  is  Accompanied  by  an  ex- 
pansion which  exercises  an  almost  irresistible  mechanical 
force;   the  effect  of  this  action  is  to  force  asunder  large 
masses  of  rock  and  destroy  the  cohesion  of  their  constituent 
particles. 

Thus,  in  all  latitudes  ana  altitudes  where  frost  occurs,  vast  waste  is  every 
season  effected.  The  student  may  note  the  effects  of  frost  on  every  plowed 
field,  and  on  every  cliff  and  railway -cutting  around  him ;  how  it  breaks  up 

QUESTIONS.— What  is  said  of  the  effect  of  winds  ?  What  is  the  origin  of  the  sandy 
tracts  along  the  sea-coast?  What  are  some  instances  of  remarkable  accumulations  of 
sand  ?  What  is  the  effect  of  freezing  •water  on  rocks  ? 


136      FIRST     PRINCIPLES     OF     GEOLOGY. 

and  pulverizes  the  soil,  cuts  away  the  cliff,  and 
FIG.  77.  jjj  ieaveSj  every  winter,  at  its  base,  a  sloping  mass 

— in  geological  language  a  talus  or  slope  of 
crumbling  fragments." 

Fig.  77  represents  a  cliff,  at  the  base  of 
which  is  a  talus,  composed  of  angular  frag- 
ments, a;  finer  particles,  b;  and  an  external 
layer  of  mud,  c* 

141.  Glaciers  (Fr.,  glace,  ice).— In  mountain  districts, 
elevated  above  the  line  of  perpetual  frost,  the  snows  are 
ever  accumulating,  inasmuch  as  the  temperature  does  not 
rise  sufficiently  for  any  considerable  proportion  to  be  melted 
and  flow  down.  These  accumulations,  in  valleys  or  other 
favorable  situations  on  the  sides  of  the  mountains,  often 
become  converted,  through  the  immense  pressure  of  the 
superincumbent  material,  into  compact  ice,  and  form  what 
are  called  glaciers,  or,  in  French,  mers  de  glace  (seas  of 
ice).f 

"The  common  form  of  a  glacier,"  says  Prof.  Forbes,  speaking  of  the  glaciers 
among  the  Alps  of  Switzerland,  "  is  a  river  of  ice  filling  a  valley  and  pouring 
down  its  mass  into  other  valleys  yet  lower.  It  is  not  a  frozen  ocean,  but  a 
frozen  torrent,  whose  origin  or  fountain  is  in  the  ramifications  of  the  higher 
valleys  and  gorges  which  descend  among  mountains  covered  with  perpetual 
snow."  Fig.  78  represents  a  view  of  the  glacier  of  Viesch,  and  Fig.  79  that 
of  Zermatt,  both  in  Switzerland;  the  latter  (as  shown  in  the  figure)  being 
formed  by  the  union  of  two  glaciers. 

Glaciers  occur,  in  Europe,  among  the  Alps,  the  Pyrenees, 

QUESTIONS. — What  are  familiar  examples  ?    What  is  a  talus  ?     What  are  glaciers  ? 
What  is  the  common  form  of  a  glacier  ? 


*  The  effect  of  frost  in  destroying  rocks  is  very  marked  in  the  polar  regions  and  on 
high  mountains.  Mr.  Scoresby,  in  his  work  on  the  Arctic  Regions,  says  of  the  rocks  of 
Spitzbergen,  "  they  appeared  solid  at  a  distance,  but  on  examination  were  found  so  full 
of  fractures  in  every  direction  that  it  was  with  difficulty  that  a  specimen  of  five  or  six 
pounds  in  a  solid  mass  could  be  obtained.  Cliffs  of  a  thousand  feet  were  found  fissured 
in  every  direction,  and  toward  the  sea-edge,  stones,  weighing  more  than  two  or  three 
ounces  each  could  not  be  obtained."  Darwin  makes  the  same  observation  on  Terra  del 
Fuego.  Here,  he  says,  he  often  observed  that  where  the  rock  was  covered  with  snow,  its 
surface  was  shivered  in  an  extraordinary  manner  into  small  angular  fragments. 

t  It  was  formerly  the  opinion  that  in  the  formation  of  a  glacier  the  snow  was  converted 
into  ice  by  alternations  of  melting  and  freezing;  but  recent  investigations  have  shown 
that  this  phenomenon  is  due  solely  to  immense  pressure.  There  Js  every  reason  to  be- 
lieve, also,  that  the  interior  of  a  glacier  is  comparatively  unaffected  by  changes  iu  the 
external  temperature.— See  Annual  Scientific  Discovery.  1860,  pp.  297. 


ATMOSPHERIC     AGENCIES.  137 

FIG.  18. 


138       FIRST      PRINCIPLES     OF     GEOLOGY. 

the  mountains  of  Norway  and  Iceland,  and  on  the  coast 
of  Spitzbergen  ;  in  Asia,  among  the  Himalaya,  Caucasus, 
and  Altai  Mountains  ;  in  Patagonia,  South  America,  and 
within  both  the  frigid  zones. 

Glaciers  have  been  chiefly  studied  in  the  Alps,  where  the  climat-3  is  suf- 
ficiently moderate  to  allow  of  their  careful  and  detailed  examination  with 
comparative  convenience.  Along  the  central  part  of  the  Alps,  from  ilout 

FIG.  79. 


Blanc  to  the  frontiers  of  Tyrol,  there  are  estimated  to  be  not  less  than  400 
glaciers,  some  of  which  fill  valleys  twenty  miles  long,  by  three  or  four  in 
width,  to  a  depth  of  600  feet.  In  the  Himalaya  Mountains,  glaciers  exist 
upon  a  most  gigantic  scale,  one  of  which,  on  the  slops  of  Kunchiujinga  (one 
of  the  highest  peaks),  is  said  to  present  at  its  termination  a  vertical  wall  of 
ice  14,000  feet  high.  It  is,  however,  in  high  Arctic  latitudes,  where  the  lino 
of  perpetual  snow  comes  down  to  the  sea  lovel,  that  the  glaciers  attain  their 

QUESTIONS.— Where  do  glaciers  occur?    Where  have  they  been  chiefly  studied  ?  What 
is  said  of  the  extent  of  some  glaciers  ? 


AQUEOUS     AGENCIES.  139 

greatest  development.  Thus,  they  were  seen  by  Dr.  Kane,  in  1855,  ap- 
parently forming  a  deep,  unbroken  sea  of  ice  over  the  whole  interior  of 
Central  Greenland,  and  sloping  gently  toward  the  coast,  where  immense 
masses  were  constantly  being  detached,  and  "  floating  off  to  be  lost  in  the 
temperatures  of  other  regions." 

142.  Motion  of  Glaciers . — " Although  apparently  solid  and  station- 
ary, glaciers  really  move  slowly  down  the  valley  or  sides  of  the  mountains, 
and  carry  with  them,  either  on  their  surface,  frozen  into  their  mass,  or  grind- 
ing and  rubbing  along  the  bottom,  all  the  fragments,  largo  and  small,  from 
blocks  many  tons  in  weight  down  to  the  finest  sand  and  mud,  that  rain  and 
ice,  and  the  friction  of  the  moving  glacier  itself  detach  from  the  adjacent 
rocks." 

The  rate  of  movement  differs  in  different  glaciers,  and  in  different  parts  of 
the  same  glacier.  Portions  of  some  glaciers  in  the  Alps  have  been  observed 
to  move,  during  the  summer,  at  the  rate  of  three  or  four  feet  per  day ;  but  in 
general,  the  advance  of  glaciers  is  very  slow,  and  can  only  be  correctly  esti- 
mated by  observations  extended  over  a  considerable  period.  The  glacier  of 
Aar,  in  Switzerland,  which  has  been  very  carefully  studied,  appears  to  have 
moved  10,000  feet  in  forty-four  years,  or  at  the  average  rate  of  375  feet  annu- 
ally. The  motion  of  glaciers  is  always  continuous  and  not  by  jerks  and 
starts. 

"With  respect  to  the  cause  of  the  motion  of  glaciers  different  views  are  en- 
tertained. Some  believe  it  to  be  due  to  a  slight  degree  of  plasticity,  a  sort 
of  semi-fluidity,  in  the  ice  mass,  by  which  it  is  enabled  actually  to  float  down 
the  declivity  by  the  action  of  gravity,  just  as  a  viscous  substance,  such  as 
partially  melted  pitch,  would  flow.  Another  theory,  advocated  by  Agassiz, 
refers  the  onward  movement  to  the  force  arising  from  the  expansion  of  water 
freezing  in  the  fissures  and  pores  of  the  ice,  into  which,  during  the  warm  sea- 
son, it  is  constantly  infiltrating ;  and,  moro  recently,  Prof.  Tyndel  and  other 
geologists  of  England  claim  to  have  proved,  that  the  motion  of  glaciers  is  the 
result  of  a  minute,  almost  molecular,  fracture  and  re- cementation  (regelation, 
as  it  is  called)  of  the  ice  particles,  which  move  as  if  they  were  sand,  continu- 
ally thawing  and  re-freezing. * 

A  glacier  descends  toward  the  base  of  the  mountain  until  the  heat  melts  it 
away.  It  usually  terminates  in  a  vertical  Avail,  which  marks  the  thickness 
of  the  ice  at  its  extremity,  and.  ia  tho  Alp*,  i.s  often  from  60  to  100  feet 
high.  During  the  summer,  currents  of  water,  formed  from  superficial  thaws, 
flow  over  the  surface  of  the  glacier,  and,  falling  into  fissures  and  chasms 

QUESTIONS. — Where  do  glaciers  attain  their  greatest  development?  Are  glaciers  fixed 
and  stationary  ?  What  is  said  of  their  rate  of  movement  ?  What  is  supposed  to  be  the 
cause  of  the  motion  of  glaciers  ?  How  far  does  a  glacier  descend  down  a  mountain  slope  ? 


*  Few  topics  in  geology  have  excited  more  interest  and  discussion  than  the  phenomena 
of  the  structure  and  movements  of  glaciers ;  and  in  some  instances  investigators — Saus- 
sure,  Agassiz,  Desor,  and  others — have  devoted  years  to  their  study,  and  have  lived 
continuously,  for  months,  in  rude  huts  erected  xipon  the  moving  ice-surface. 


140       FIRST     PRINCIPLES     OF     GEOLOGY. 

which  extend  across  it,  issue  as  a  single  stream  from  a  sort  of  vault  or  cavern 
at  its  termination.  Such  streams,  from  the  glaciers  of  the  Alps,  constitute  the 
source  of  supply  of  some  of  the  principal  rivers  of  Europe.  . 

The  terminus  of  a  glacier, 'however,  varies  somewhat  with  the  seasons, 
being  lower  in  winter  than  in  summer.  In  cold  seasons  it  sometimes  invades 
the  habitable  valleys  of  Switzerland,  and  irresistibly  and  imperceptibly  ad- 
vances upon  and  destroys  the  cottages  and  farms  of  the  peasantry.  "The 

FIG.  80. 


green  forests  slowly  disappear  before  it,  and  the  growing  wheat  almost  feels 
its  icy  touch  before  the  soil  is  lifted  by  the  ruthless  plowshare.  Whea,  after 
such  an  advance,  a  warm  summer  succeeds,  and  the  glacier  retreats  to  its 
former  bounds,  the  surface  it  covered  is  found  to  be  changed  into  a  dreary 
waste  of  loose  rocks  and  stones.  These  have  originally  fallen  upon  the 
glacier,  and  have  been  borne  down  and  deposited  by  its  melting." 

The  confused  heaps  or  ridges  of  rock  fragments,  mud, 
and  sand,  which  a  glacier  pushes  before  it,  or  carries  upon 
its  surface,  have  received  the  name  of  moraines. 

Fig.  78  gives  a  clear  idea  of  the  nature  of  these  accumulations  of  detritus, 

QUESTIONS.— What  is  its  usual  termination?     Docs  a  glacier  ever  invade  habitable 
valleys  ?    What  is  the  condition  of  the  ground  temporarily  covered  by  a  glacier  ?    What 
has  been  given  to  the  heaps  of  stone  and  earth  accumulated  by  glaciers? 


AQUEOUS     AGENCIES. 


141 


and  the  manner  in  which  they  collect  in  long  lines  upon  the  surface  of  the 
glacier,  in  the  direction  of  its  motion.  Fig.  80,  representing  the  glacier  of  the 
Aar,  shows  how,  when  two  glaciers  unite,  separate  lines  of  moraine  also  come 
together  and  float,  as  it  were,  down  the  middle  of  the  common  glacier.* 

FIG.  81 


The  quantity  of  stony  material,  and  the  enormous  size  of  the  masses  of 
rock  transported  by  glaciers  can  hardly  be  appreciated  from  any  description. 

QUESTION. — What  is  said  of  the  amount  of  detritus  transported  by  glaciers  ? 

*  Concerning  the  pole  attached  to  a  rock,  seen  in  the  engraving,  Fig.  SO,  Agassiz,  in  hia 
"Etudes  stir  les  Glaciers"  (from  which  the  illustration  is  taken),  relates  the  following 
incident :  A  certain  explorer  fastened  the  pole  to  a  large  mass  of  rock  on  the  surface  of  a 
glacier,  high  up  toward  its  source,  and  carefully  recorded  the  fact  in  a  published  ac- 
count of  his  investigations.  Some  ten  years  after,  another  explorer  searched  for  the  pole 
and  block,  and  found  that  it  had  traveled,  in  the  interval,  some  eight  or  ten  miles  toward 
the  termination  of  the  glacier.  The  same  figure  also  shows  how  tabular  masses  of  rock, 
by  protecting  the  ice  beneath  them  from  the  melting  action  of  the  sun,  are  gradually  lifted, 
by  the.  waste  of  the  exposed  surface  upon  a  pedestal  or  stem  of  ice,  and  at  the  same  timo 
are  moving  with  the  general  mass  toward  a  lower  leveL 


142        FIRST     PRINCIPLES     OF     GEOLOGY. 

Sometimes  the  ice  is  almost  concealed  by  the  accumulated  piles  of  stone  that 
cover  it.  Prof.  Forbes  relates  that  he  saw,  in  one  of  the  valleys  of  Switzer- 
land, a  rock  brought  down  by  a  glacier,  the  dimensions  of  which  were  nearly 
a  hundred  feet  in  length  and  from  forty  to  fifty  in  height. 

The  rocks  upon  and  against  which  the  glaciers  have  pressed  are  found, 
wherever  exposed  to  view,  to  be  smoothed  and  scratched  (striated,  as  it  is 
termed),  and  occasionally  marked  with  deep  grooves  and  furrows.  These 
effects  are  mainly  due  to  the  friction  of  sand  and  angular  fragments  of  rock 
embedded  in  the  ice,  and  driven  forward,  under  enormous  pressure,  by  the 
motion  of  the  glacier.  The  grooves  and  strise  thus  produced  are  parallel  to 
each  other,  and  also  correspond  in  direction  with  the  movements  of  the  glacier ; 
but  as  the  motion  of  the  glacier  changes,  new  sets  of  scratches  will  be  pro- 
duced, which  sometimes  cross  those  previously  made,  at  a  high  angle. 

Fig.  81,  which  is  an  actual  sketch,  drawn  by  Prof.  Forbes,  represents  granite 
blocks  jammed  in  between"  the  ice  of  a  glacier  and  the  rock,  in  the  process  of 
grinding  down  and  grooving  the  retaining  walL 

FIG.  82. 


Fig.  82  represents  a  specimen  of  a  rock  thus  smoothed  and  striated  by  rm. 
Alpine  glacier. 

143.  Icebergs,— In  the  Polar  regions,  glaciers  descend  to 
the  sea-coast,  and  even  advance  into  the  sea,  so  that  their 
extremities  often  become  separated  from  the  main  mass, 
and  float  away  as  icebergs. 

Let  a,  5,  c,  d  and  e  (Fig.  83)  represent  a  section  of  a  coast,  along  a  ravine  or 
hollow,  in  which  a  glacier,/  g,  c,  finds  its  way  outward  to  the  sea,  s;  the 
mass  of  ice  at  its  extremity  being  lighter  than  water,  has  a  tendency  to  float, 
and  the  movement  of  the  waves  and  tides  assisting,  large  fragments  (m)  readily 
become  detached  from  the  glacier  and  are  floated  off  by  currents. 

Icebergs  thus  formed  vary  from  a  few  yards  to  miles  in  circumference,  and 
often  rise  from  200  to  300,  or  even  500  feet,  above  the  surface  of  the  ocean. 
But  as  ice  floats  with  eight-ninths  of  its  bulk  below  the  surface,  the  greater 

QTjESTioNS.—What  is  the  mechanical  action  of  glaciers  ?  "What  is  said  of  the  formation 
of  icebergs  ? 


AQUEOUS     AGENCIES. 


143 


portion  of  an  iceberg  must  always  be  concealed  from  observation;  and  a 
height  of  200  to  300  feet  above  the  surface  of  the  ocean  would  necessarily 
imply  a  vertical  depth  of  from  2,000  to  3,000  feet  below  it. 


FIG.  83. 


Fig.  84  represents  an  iceberg  seen  by  Capt.  Parry,  the  size  of  which  may 
be  inferred  by  comparison  with  the  ship  in  proximity  to  it.  Capt.  Ross  saw 
icebergs  aground  iu  Baffin's  Bay,  where  the  depth  of  water  exceeded  1,500 
feet.  One  seen  by  the  French  Exploring  Expedition,  in  the  Southern  Ocean, 
in  1840,  was  thirteen  miles  long,  with  vortical  walls  IOC  feet  high. 

FKJ.  84. 


Icebergs  very  frequently  carry  great  quantities  of  rock 
and  earth  from  the  lands  where  the  bergs  were  formed  as 
portions  of  glaciers,  to  new  localities  in  warmer  latitudes. 

QTTESTIONS.— What  is  said  of  the  size  of  icebergs  ?  What  proportion  of  an  iceberg 
floating  is  exposed  to  view  ?  Do  icebergs  act  as  carriers  of  rock  material  ? 


144        FIRST     PRINCIPLES     OF     GEOLOGY. 

Captain  Scoresby  conjectures  that  a  group  seen  by  him  in  the  Northern 
Ocean  were  loaded  with  from  50,000  to  100,000  tons  of  loose  materials.  Dr. 
Kane  also  describes  the  ice-belt  which  lines  the  shores  of  Smith's  Strait, 
Baffin's  Bay  (and  which,  in  summer,  becomes  detached  and  floats  off),  as 
covered,  in  some  localities,  "  with  millions  of  tons  of  rubbish  ; — greenstones, 
limestones,  slates,  rounded,  angular,  massive,  and  ground  to  powder."  He 
also  observed  rafts  of  ice  thus  loaded  with  large  angular  blocks  and  bowlders 
floating  many  miles  out  at  sea.  Pig.  85  represents  one  of  these  ice-rafts, 
figured  by  Dr.  Kane,  loaded  with  masses  of  slate.x 

FIG.  85. 


Icebergs  from  Baffin's  Bay  frequently  float,  before  melting,  as  far  south  as 
40°  north  lat,  (or  about  the  latitude  of  New  York  City) ;  in  one  instance,  an 
iceberg,  with  bowlders  upon  it,  was-  seen  on  the  Atlantic,  in  lat.  36°  N.  (or 
nearly  as  far  south  as  Cape  Hatteras). 

Whenever  icebergs  dissolve  it  is  evident  that  their  freight  of  earth  and 
rock  will  fall  to  the  bottom  of  the  sea;  and  in  this  manner  submarine  moun- 
tains, plains,  and  valleys  may  become  strewed  over  with  gravel,  sand,  mud, 
and  fragments  of  rock,  transported  from  very  distant  localities,  and  of  a  nature 
dissimilar  from  all  in  the  vicinity. 

Icebergs  are  often  stranded,  even  in  comparatively  deep  water.  "When 
this  happens,  the  disturbances  occasioned  on  the  sea-bott'om,  by  the  rubbing 
or  thumping  of  such  bodies,  weighing  perchance  millions,  or  hundreds  of  mil- 
lions of  tons,  and  impelled  by  powerful  currents,  must  obviously  be  very 
great.  We  may  conceive  that  the  power  thus  exerted  would  be  amply  suf- 
ficient to  furrow  and  pulverize  rocks,  excavate  valleys,  and  perhaps  even 
crush  and  disrupt  submarine  hills  and  ridges. 

From  the  above  facts,  it  seems  probable  that  if  the  bed  of  the  ocean,  in 
both  the  northern  and  southern  hemispheres,  between  the  fortieth  and  sixtieth 
degrees  of  latitude,  could  be  exposed  to  view,  its  rock-surface  would  be  every- 
where smoothed  and  striated  by  the  ice-bergs  which  have  dragged  over  it, 

QTJHSTIOXS. — What  are  some  examples?  To -what  distances  do  icebergs  thus  loaded 
float?  What  takes  place  when  they  dissolve?  What  effects  may  icebergs  produce  upon 
the  sea-bottom  ?  What  would  probably  be  the  condition  of  the  beds  of  the  northern  and 
southern  oceans,  if  exposed  to  view  ? 


AQUEOUS     AGENCIES.  145 

and  also  strewed  with  sand,  gravel,  and  bowlders,  drifted  from  the  Arctic  and 
Antarctic  regions. 

Icebergs  may  also  exercise  an  influence  upon  climate.  Those  which  drift 
from  Baffin's  Bay  along  our  own  coast,  sensibly  cool  the  waters  of  the  Gulf 
Stream  for  forty  to  fifty  miles  around,  and  the  temperature  of  the  air  on  ap- 
proaching them  has  been  known  to  fall  17°  to  18°  P.  When  driven,  as  they 
sometimes  are,  in  large  numbers  into  Hudson's  Bay,  they  produce  intense 
cold,  and  modify  the  seasons  over  the  northern  portion  of  the  American  con- 
tinent. In  the  southern  hemisphere,  icebergs  drift  much  nearer  the  equator 
than  in  the  northern,  and  are  occasionally  seen  off  the  Cape  of  Good  Hope, 
in  latitude  36°.  "Were  they  not  checked  before  reaching  a  corresponding 
latitude  in  the  Northern  Ocean  they  might  float  into  the  Mediterranean,  and 
chill  the  waters  of  that  sea  to  such  an  extent  as  to  produce  a  marked  change 
in  the  climate  of  the  adjacent  countries. 

Apart  from  the  interest  which  pertains  to  glaciers  and  icebergs,  as  import- 
ant causes  of  change  in  the  condition  of  the  earth's  surface,  the  study  of 
their  phenomena  has  furnished  a  key  to  the  solution  of  some  of  the  most  in- 
teresting and  important  problems  in  geology,  and  for  this  reason  (as  will  bo 
shown  hereafter)  they  merit  especial  attention  from  the  student. 

144.  Springs,— Springs,  which  are  discharges  of  water 
from  the  earth,  effect  geological  changes,  by  wearing 
and  transporting,  or  dissolving  and  re-depositing  min- 
eral matter. 

The  mineral  substances  most  abundantly  precipitated  from  water,  viz., 
travertin,  tufas,  stalactite,  stalagmite^  silicious  sinter,  and  bog-iron  ore,  have 
been  already  noticed.  (See  §§  63,  64,  67,  71.) 

Origin  of  Springs,— The  water  of  springs  and  wells  is 
derived  from  rain. 

This,  falling  upon  the  surface  of  the  earth,  sinks  downward  through  the 
loose  and  porous  soil  or  rock,  until  it  reaches  a  bed  of  clay  or  rock  imperme- 
able to  water.  Here,  it 
either  accumulates  and  sat- 
urates the  soil,  or  else  run- 
ning along  the  surface  of 
the  impervious  stratum,  it 
bursts  out  at  some  point 
where  such  impervious  bed 
or  stratum  comes  to  the  surface  in  consequence  of  a  valley  or  depression. 
In  such  a  case,  the  flow  of  water  constitutes  a  spring.  Thus,  suppose  a, 
(Fig.  86)  to  be  a  hill  of  sand  or  gravel,  resting  upon  a  stratum  of  clay,  b;  then 

QUESTIONS. — Do  icebergs  exercise  any  influence  upon  climate  ?  Show  this  by  illustra- 
tive facts?  How  do  springs  effect  geological  changes?  What  mineral  substances  are 
most  abundantly  deposited  by  springs  ?  What  is  the  source  of  the  water  of  springs  and. 
wells? 

7 


146       FIRST     PRINCIPLES     OF     GEOLOGY. 

the  water,  percolating  through  the  upper  permeable  bed,  would  finally  reach 
the  impervious  stratum  and  run  along  its  surface  until  it  found  an  outlet  at 
c,  the  foot  of  the  hill,  where  a  spring  would  be  formed. 

If  there  are  no  irregularities  in  the  surface  of  the  impervious  strata  so 
situated  as  to  allow  a  spring  to  burst  forth,  the  water,  soaking  downward, 
will  not  drain  off,  but  will  accumulate,  and  rise  among  the  particles  of  soil,  as 
it  would  among  shot  or  bullets  in  a  water-tight  vessel.  If  a  hole  or  pit  be 
dug  into  such  earth,  reaching  below  the  level  of  the  water  accumulated  in  it, 
it  will  soon  be  filled  up  with  water  to  this  level,  and  will  constitute  a  well. 
The  reason  why  some  wells  are  deepdr  than  others,  is,  that  the  distance  of 
the  impervious  stratum  below  the  surface  is  different  in  different  localities. 

145.  Artesian  Wells, — In  many  localities,  if  the  strata 
be  penetrated  to  a  considerable  depth  by  boring,  a  supply 
of  water  will  sometimes  rise  with  great  force  to  the  sur- 
face, and  continue  to  flow  uninterruptedly.  Such  excava- 
tions are  termed  "  Artesian  Wells/'  from  the  province  of 
Artois,  in  France,  where  this  plan  for  obtaining  water  is 
believed  to  have  originated. 

The  theory  of  the  rise  of  water  in  artesian  wells  will  be  readily  understood 
from  the  following  diagram,  Fig.  8t.  Suppose  M  M,  a  stratum  of  sand  or 
some  other  material  pervious  to  water,  to  be  inclosed  between  other  strata, 

FIG.  87. 


A  and  B,  which  are  impervious ;  and  that  all  the  strata  are  at  the  same  time 
so  inclined  as  to  form  a  sort  of  basin.  Then,  the  water  which  falls  upon  the 
uncovered  margin  or  outcrop  of  the  porous  strata  M  will  be  absorbed  and 
sink  to  the  lower  portion  of  the  basin,  where  it  will  be  prevented  from  aris- 
ing to  the  surface  by  the  impervious  stratum  above  it,  and  from  sinking 

QUESTIONS. — Illustrate  the  formation  of  springs  and  wells.     Wh:it  arc  artesian  -wells? 
Explain  their  theery. 


AQUEOUS     AGENCIES.  147 

lower,  by  the  equally  impervious  strata  below  it.  It  will,  therefore,  accumu- 
late, as  in  a  reservoir.  If  now  we  bore  down  through  the  upper  stratum, 
until  we  reach  the  stratum  containing  the  water,  the  water  will  rise  in  the 
excavation  to  a  certain  height,  proportional  to  the  height  or  level  of  the 
water  accumulated  in  the  reservoir  Jf,  from  which  it  flows. 

The  great  depths  to  which  artesian  wells  have  been  sunk  have  already  been 
noticed.  (See  §§  8  and  111.) 

The  water  supply  afforded  by  some  of  them  is  also  very  great.  One  at 
Grenelle,  near  Paris,  1800  feet  deep,  is  capable  of  supplying  water  at  the  rate 
of  600,000  gallons  per  day;  and  the  district  of  country  over  which  this  water 
was  precipitated  as  rain,  judging  from  the  curvature  of  the  strata  through 
which  the  excavation  was  made,  is  estimated  to  be  200  miles  or  more  distant 
from  the  point  where  the  water  issues.  An  artesian  well,  at  Louisville,  Ky., 
excavated  in.  1859,  discharges  333,000  gallons  every  twenty-four  hours— the 
water  rising  (in  pipes),  by  its  own  pressure,  170  feet  above  the  surface. 

14G.  MJneral  Springs. — Spring- water,  although  it  maybe  perfectly 
transparent,  always  contains  more  or  less  of  mineral  matter  dissolved  in  it. 
The  nature  of  the  substances  will  of  course  vary  with  the  character  of  the 
soil  through  which  the  water  percolates.  The  most  usual  impurities  are  car- 
bonate of  lime,  common  salt,  sulphate  of  lime  (gypsum),  sulphate  and  carbon- 
ate of  magnesia,  and  compounds  of  iron. 

When  the  waters  of  springs  retain  in  solution  so  large  a  proportion  of 
mineral  or  gaseous  matter  as  to  give  them  a  decided  taste,  they  are  termed 
mineral  icaters,  and  arc  usually  reputed  to  have  some  medicinal  quality, 
varying  with  the  nature  of  the  substance  in  solution. 

"Waters  which  contain  iron  in  quantity  sufficient  to  impart  to  them  an  inky 
taste  are  termed  chalybeate;  the  iron  exists  in  the  water  most  frequently  in 
the  state  of  carbonate  dissolved  in  carbonic  acid,  and  rarely  in  a  proportion 
exceeding  one  grain  in  a  pound  of  water. 

"Waters  impregnated  with  sulphuretted  hydrogen  gas  aro  termed  sidphurous 
or  sulphuretted;  they  may  be  readily  recognized  by  their  nauseous  taste  and 
odor.  Eemarkable  springs  of  this  characloi  exist  at  Sharon,  New  York,  and 
also  in  Virginia. 

In  somo  springs  carbonic  acid  is  very  abundant,  and  imparts  to  the  water 
an  effervescent,  sparkling  character,  liko  that  noticed  in  the  "  Seltzer"  and 
"  Saratoga"  waters. 

Light  carburetted  hydrogen  (illuminating  gas)  is  also  evolved  from  spring?, 
in  some  instances.  At  Kenawha,  in  Virginia,  it  rises  in  immense  quantities, 
in  connection  with  salt  water,  from  artesian  wells,  and  being  conducted  by 
an  arrangement  of  pipes  under  the  salt-boilers,  furnishes  sufficient  heat  by 
its  combustion  to  evaporate  the  brine.  A  similar  natural  supply  of  this  gas, 

QUESTIONS.— To  what  depths  have  artesian  wells  been  excavated  ?  What  is  said  of 
the  supply  of  water  afforded  by  them  ?  What  is  said  of  the  purity  of  spring  waters  ? 
When  are  springs  termed  mineral  ?  What  are  chalybeate  springs?  "What  are  sulphur- 
etted ?  What  is  said  of  the  presence  of  gas  in  some  springs  ? 


148       FIRST     PRINCIPLES     OF     GEOLOGY. 

in  the  town  of  Fredonia,  in  New  York,  has  for  many  years  past  been  ex- 
tensively applied  for  illuminating  purposes. 

147.  Saline  Springs,— Springs,  whose  waters  contain  a 
large  proportion   of  earthy  or  alkaline   salts,  are   called 
saline,  although  this  term  is  generally  used  to  designate 
particular  springs  containing  common  salt. 

These  last,  considered  in  an  economical  point  of  view,  are  the  most  im- 
portant of  all  mineral  springs.  They  occur  in  all  parts  of  the  world,  and 
their  waters  are  extensively  evaporated  for  the  purpose  of  obtaining  salt. 

In  the  United  States,  salt  springs  of  value  occur  in  New  York,  Virginia, 
Ohio,  Pennsylvania,  Illinois,  Michigan,  Missouri,  Arkansas,  the  Territory  of 
Utah,  and  in  Canada.  The  amount  of  salt  contained  in  these  waters  varies 
from  ten  to  thirty-five  per  cent.  In  many  localities  where  salt  springs 
occur,  great  additional  supplies  of  brine  have  been  obtained  by  boring ;  and 
in  Virginia  and  Ohio  excavations  have  been  made  for  this  purpose  to  the 
depth  of  1,000  to  1,200  feet. 

The  quantity  of  salt  manufactured  from  the  waters  of  salt  springs  hi  the 
United  States,  in  1856,  was  about  12,000,000  bushels.  Of  this  quantity 
the  salt  springs  of  Oriondaga  County,  N.  Y.,  furnished  about  6,000,000  bush- 
els; those  of  Virginia,  3,800,000;  of  Ohio,  1,500,000;  of  Illinois,  50,000; 
of  Michigan,  10,000;  of  Pennsylvania,  900,000.  The  waters  of  the  Onon- 
daga  salt  springs  contain  about  one-seventh  part  of  their  weight  of  dry  salt ; 
and  the  supply  of  water  is  not  less  than  2,000,000  gallons  per  day  for  six 
months  in  the  year.* 

The  amount  of  salt  contained  in  sea- water  is  about  twenty-seven  per  cent. ; 
which  amounts  to  nearly  four  ounces  per  gallon,  or  a  bushel  in  from  300  to 
350  gallons.  At  Nantucket,  where  salt  is  made  from  sea-water  by  solar 
evaporation,  350  gallons  of  water  are  required  to  yield  a  bushel ;  while  at 
Onondaga  forty-one  to  forty-five  gallons  suffice. 

Numerous  lakes  of  salt  water  are  found  scattered  over  the  territory  of  the 
United  States,  between  the  Mississippi  and  the  Pacific.  Of  these  the  most 
famous  and  extensive  is  the  Great  Salt  Lake  of  Utah,  whose  waters  contain 
22,000  grains  of  salt  to  the  gallon,  or  nearly  one-third  of  their  whole  weight. 

148.  Origin  of  Salt  Springs,  Lakes,   etc,— Salt  springs 
undoubtedly    originate    from    the    percolation   of    water 

QTTESTIONS. — "What  are  saline  springs  ?  What  mineral  springs  are  the  most  important  ? 
Where  do  salt  springs  occur  in  the  United  States  ?  What  amount  of  salt  is  manufactured 
from  them  ?  What  proportion  of  salt  is  contained  in  sea-water  ?  What  is  said  of  the  ex- 
istence of  salt  lakes  ?  What  is  the  probable  origin  of  salt  springs? 


*  The  amount  of  salt  yearly  consumed  in  the  United  States  (for  various  uses)  is  esti- 
mated at  sixty  pounds  for  each  inhabitant,  or  a  total  of  25,000,000  of  bushels.  Of  thin 
quantity  nearly  one-half  is  imported  from  foreign  countries. 


AQUEOUS     AGENCIES.  149 

through  subterranean  beds  of  rock-salt,  or  through  strata 
containing  a  large  proportion  of  salt. 

It  is  an  error,  however,  to  attribute  the  saltness  of  the  sea  to  the  presence 
of  vast  beds  of  mineral  salt  at  its  bottom;  for  the  sea  undoubtedly  owes  all 
its  salts  to  washings  from  the  land.  The  streams  that  have  flowed  into  it  for 
ages  have  been  constantly  bringing  soluble  mineral  matters  from  the  land, 
and  as  pure  water  alone  evaporates  from  the  surface  of  the  ocean,  the  quan- 
tity of  such  matter  has  been  continually  accumulating,  until  the  whole  ocean 
has  acquired  its  present  briny  and  bitter  condition.  The  evidence  on  this 
point  is  conclusive ;  and  the  saline  condition  of  sea- water  is  but  an  exaggera- 
tion of  that  of  all  ordinary  lakes,  rivers,  and  springs.  These  all  contain 
more  or  less  of  the  mineral  constituents  of  sea- water,  but  as  their  waters  are 
continually  changing  and  flowing  into  the  sea,  the  salts  in  them  do  not  ac- 
cumulate. 

Again,  every  lake  into  which  rivers  flow,  and  from  which  there  is  no  out- 
let except  by  evaporation,  is  a  salt  lake ;  and  it  is  extremely  curious  to  ob- 
serve that  this  condition  disappears  when  an  artificial  outlet  is  provided. 
Examples  of  such  lakes  are  the  Dead  Sea,  the  Caspian,  the  Sea  of  Aral,  and 
the  Great  Salt  Lake  of  Utah,  the  saltuess  of  all  of  which  greatly  exceeds  that 
of  the  ocean. 

149.  Streams  and  Rivers,  as  agents  for  producing  geo- 
logical changes,  act  chiefly  in  a  mechanical  way,  and  their 
influence  depends  partly  on  the  nature  of  the  rocks  over 
which  they  run,  the  rapidity  of  their  flow,  and  the  volume 
of  water. 

If  the  rocks  over  which  they  pass  are  of  a  soft  and  friable  material  they 
soon  cut  out  channels  and  transport  the  abraded  material  in  the  state  of  mud, 
sand,  and  gravel,  to  the  lower  level  of  some  lake,  or  to  the  bed  of  the  ocean. 
It  may  be  generally  observed  that  a  river  will  have  its  rapids  at  the  locali- 
ties where  the  hardest  strata  or  rock-material  occur;  as  these  resist  the 
wearing  action  of  the  water  for  a  longer  period  than  the  other  portions  of  the 
river-bottom.  Thus,  the  first  waterfalls  of  the  Eappahannock,  James,  Neuse, 
and  other  rivers  of  Virginia  and  North  Carolina,  indicate  where  a  ridge  of 
granitic  rocks  comes  up  to  the  surface. 

150.  The  eroding,  as  well  as  the  transporting  power  of 
streams  and  rivers,  is  greatly  aided  by  the  rapidity  of  their 
currents. 

QUESTIONS.— To  what  is  the  saltness  of  the  sea  probably  due  ?  Under  what  circum- 
stances will  a  lake  become  salt?  How  do  streams  and  rivers  produce  geological 
changes?  At  what  point  in  the  course  of  a  river  will  rapids  occur ?  What  effect  has 
the  velocity  of  a  river  on  its  eroding  power  ? 


150       FIRST     PRINCIPLES     OF     GEOLOGY. 

Thus,  it  has  been  calculated,  for  example,  that  the  velocity  of  three  inches 
per  second  will  tear  up  fine  clay ;  that  six  inches  will  lift  fine  sand ;  eight 
inches,  sand  as  coarse  as  linseed ;  and  twelve  inches,  fine  gravel ;  while  it  re- 
quires a  velocity  of  twenty-four  inches  per  second  to  roll  along  rounded  pebbles 
an  inch  in  diameter,  and  thirty-six  inches  per  second  to  sweep  angular  stones 
of  the  size  of  a  hen's  egg.  The  following  statement  of  a  law,  determined  by 
Mr.  W.  Hopkins  of  England,  also  illustrates  how  rapidly  the  size  of  water- 
borne  fragments  increases  in  proportion  to  the  velocity  of  the  moving  water : 

The  power  of  water  to  move  bodies  that  are  in  it  in- 
creases as  the  sixth  power  of  the  velocity  of  the  current. 

Thus,  if  we  double  the  velocity  of  a  current,  its  motive  power  is  increased 
sixty-four  times;  if  its  velocity  be  multiplied  by  three,  its  motive  power  will 
be  increased  729  times;  if  by  four,  2,048  times;  and  so  on.  In  estimating 
the  mechanical  force  of  water  it  is  also  necessary  to  bear  in  mind  that  all 
rocks  and  stones  lose  fully  one- third  of  their  weight  when  suspended  in 
water;  and  this  consideration  will  enable  us  to  understand  more  readily 
how,  in  great  storms,  rocks  weighing  tons  are  sometimes  carried  to  a  con- 
siderable distance  by  the  action  of  waves  or  torrents. 

The  eroding  power  of  rivers  is  also  greatly  assisted  by  the  materials  me- 
chanically suspended  in,  or  forced  onward,  by  the  water — every  particle  of 
sand,  every  pebble  or  rock,  rasping  and  grinding  still  deeper  and  deeper  the 
channels  down  which  they  are  borne.  As  familiar  illustrations  of  this  action 

we  may  instance  the  vertical  holes  drilled 
in  rocks  by  means  of  pebbles  so  situated 
that  a  rotary  action  is  given  them,  each 
in  one  place,  by  water  in  motion.  These, 
which  are  commonly  termed  "  pot-holes," 
may  be  found  in  most  situations  where  a 
stream  of  water  falls  upon  a  rock  bottom. 
A  pebble  gets  so  established  in  an  eddy, 
that  it  remains  there,  and  by  constant 
friction  works  a  vertical  hole  downward, 
sometimes  to  the  depth  of  several  feet. 
In  some  instances,  where  the  bed  of  the  stream  has  been  lowered  by  erosive 
action,  sections  of  these  cavities  are  shown,  as  in  Fig.  88. 

151.  Valleys  excavated  from  strata,  by  the  action  of 
running  water,  are  termed  valleys  of  erosion  (erosus, 
gnawed  away). 

Of  these,  some  very  remarkable  examples  exist  in  our  own  country.  A 
few  may  be  cited  in  the  way  of  illustration. 

QUESTIONS. — Illustrate  this.  How  does  the  power  of  water  to  move  bodies  increase  ? 
What  circumstances  assist  the  mechanical  action  of  water?  What  is  the  origin  of  tho 
so-called  "pot-holes ?"  What  are  valleys  of  erosion  ? 


AQUEOUS     AGENCIES. 


151 


The  Falls  of  Niagara  are  150  feet  in  height,  and  tha 
average  amount  of  water  passing  over  each  minute  is  esti- 
mated at  670,000  tons.  This  water,  by  its  abrading  power, 
has  undoubtedly  excavated  for  itself  the  gorge  or  channel — 
seven  miles  long,  200  feet  deep,  and  1,200  to  2,000  feet 
wide — which  now  intervenes  between  the  Falls  and  Lake 
Ontario.  The  minimum  time  required  to  wear  through  this 
space  has  been  estimated,  by  Sir  Charles  Lyell,  at  35,000 
years.  At  present  the  Falls  are  supposed  to  recede  at  an 
average  rate  of  about  one  foot  per  annum. 

An  examination  of  the  rocks  over  which  the  Niagara 
River  flows,  from  Lake  Erie  to  Lake  Ontario,  enables  us  to 
understand  the  present  operations  of  the  Falls,  and  also  to 
estimate  their  future  action.  The  nature  and  position  of 
these  rocks  are  clearly  shown  on  tho  sides  of  the  ravine 
excavated  by  the  Falls,  and  also  in  the  ideal  section  given 
in  Fig.  89,  in  which / represents  the  Falls;  I,  g,  h,  the  level 
of  Lake  Erio ;  5,  c,  d,  f,  the  course  of  the  Niagara  River ; 
a,  Lake  Ontario  ;  and  m,  the  city  of  Lewiston.  The  strata 
through  which  the  Falls  have  cut  their  way  consist  of 
limestones,  4  (Niagara  limestone) ;  soft  shales,  3  (Niagara 
shales) ;  and  sandstones,  2  (Medina  sandstone) ;  all  of  which 
are  inclined,  or  dip  to  the  south,  as  shown  in  the  section. 
This  inclination  of  the  strata  favors,  at  present,  the  recession 
of  the  Falls,  inasmuch  as  the  uppermost  rock,  over  which 
the  water  is  precipitated,  is  a  hard  limestone,  ninety  feet 
thick,  while  tho  lower  rock,  supporting  the  limestone  and 
forming  the  base  of  the  cliff,  is  a  soft  and  friable  shale.  This 
last  being  easily  worn  away  by  the  action  of  the  water  and 
by  frost,  leaves  the  superincumbent  limestone  unsupported, 
and  large  masses  of  it  occasionally  fall  by  their  own  weight. 
The  well-known  "  Table  Rock"  Is  a  portion  of  the  upper 
limestone,  which  has  assumed  a  tabular  appearance  by  the 
removal  of  the  shales  beneath  it. 

An  examination  of  the  section  will  also  show  that  if  the 
Falls  continue  to  recede,  the  inclination  of  the  rocks  will 
soon  carry  the  shales  (3)  so  far  below  the  bed  of  the  Nia- 
gara River  that  they  will  cease  to  be  acted  upon.  When 
this  happens,  the  hard  limestone  now  at  the  top  of  the  Falls 
will  also  constitute  their  base,  and  the  excavating  process 
will  be  essentially  retarded. 

Upon  the  Genesee  River,  N.  Y.,  the  water  has  excavated 
for  itself  a  channel,  in  solid  rock,  which  in  some  places  ex- 

QTJESTIONS.— What  is  said  of  the  erosive  action  of  water  exhibited 
at  the  Falls  of  Niagara  ?  What  are  other  illustrations  ? 


152      FIRST     PRINCIPLES     OF      GEOLOGY. 

ceeds  300  feet  in  depth.  At  Trenton  Falls,  N.  Y.,  limestone  rocks  may  be 
seen  cut  through  to  the  depth  of  100  to  200  feet ;  and  at  the  Great  Falls  of 
the  Potomac,  near  "Washington,  a  gorge  has  been  worn,  by  water,  in  hard 
mica  schist,  four  miles  long  and  from  sixty  to  seventy  feet  deep. 

But  the  most  striking  examples  of  the  erosive  power  of  water  are  the  so- 
called  canons — (pronounced  lian-yari)* — or  deep  gulfs  excavated  by  some  of  the 
rivers  of  the  southwestern  portion  of  our  country.  The  dimensions  of  some  of 
these  valleys  of  erosion,  as  given  by  recent  explorers,  seem  almost  incredi- 
ble, and  certainly  have  no  parallel  elsewhere.  Thus,  a  canon,  explored  by 
Capt.  Marcy,  U.S.  A.,  upon  the  Bed  River  of  Texas,  is  seventy  miles  long, 
with  precipitous  banks  of  rock  from  500  to  800  in  height.  Another,  upon  tho 
Canadian  River,  is  fifty  miles  in  length  and  250  feet  deep.  But  even  these 
seem  insignificant  wnen  compared  with  the  excavation  made  by  the  Colorado 
•River  and  its  tributaries  in  the  table-lands  of  California,  which  are  described 
in  the  report  of  the  Expedition  of  Lieut.  Ives  (1858),  as  exceeding,  in  some 
instances,  a  mile  in  depth.  The  streams  flowing  through  these  immense  gulfs 
are  generally  inaccessible  from  above,  and  the  traveler  who  meets  with  a 
canon  in  crossing  the  plains  is  sometimes  obliged  to  journey  for  days  beside 
it  before  finding  an  opportunity  to  cross  or  even  to  descend  to  tho  water  at 
its  bottom. 

152.  Although  rivers  with  rapid  currents  are  continually 
modifying  or  deepening  their  channels,  yet  the  general 
form  and  direction  of  river-courses  are  determined  by  other 
causes  than  the  agency  of  the  river  itself.  In  other  words, 
"rivers  are  not  the  producers,  in  the  first  instance,  of  their 
own  valleys/' 

This  proposition  will  be  more  readily  understood  by  the  following  illustra- 
tion, given  by  Mr.  Jukes:  "If  we  watch,"  says  he,  "  the  tide  receding  from 
a  fiat,  muddy  coast,  we  should  see  that  the  mud-flat,  even  where  no  fresh 
water  drains  over  it  from'  tho  land,  is  frequently  traversed  by  a  number  of 
little  branching  systems  of  channels,  opening  one  into  tho  other,  and  tending 
to  a  general  embouchure  on  the  margin  of  the  mud-flat,  at  low  water-mark. 
The  surface  of  the  mud  is  not  a,  geometrical  plane,  but  slightly  undulating ; 
and  the  sea,  as  it  recedes,  carries  off  some  of  the  looser  surface  matter  from 
some  parts,  thus  making  additional  hollows,  and  forming  and  giving  direction 
to  currents  which  acquire  more  and  more  force,  and  are  drawn  into  narrower 
limits  as  the  water  falls.  Deeper  channels  are  thus  eroded,  and  canals  sup- 
plied for  the  drainage  of  tho  whole  surface,  which  is  immediately  directed 
into  them.  First  two,  and  then  more  of  these  little  systems  of  drainage 
unite,  until  at  dead  low  water  wo  often  have  the  minature  representation  of 

QUESTIONS.— Describe  the  "canons"  of  the  southwestern  States.  Is  a  river's  course 
and  form  determined  by  its  own  action  ?  Illustrate  the  manner  in  which  the  river  sys- 
tems of  continents  have  originated. 


AQUEOUS     AGENCIES.  153 

the  river  system  of  a  great  continent  (wanting  of  course  the  mountain  chains), 
produced  before  our  eyes  in  the  course  of  a  single  tide,  in  the  very  manner 
and  by  the  very  agents  by  which  all  river  systems  on  all  islands  and  conti- 
nents have  been  produced.  The  difference  between  them  is  this  only,  that 
our  islands  and  continents  are  now  above  the  sea,  not  in  consequence  of  the 
gradual  fall  of  the  water,  but  in  consequence  of  the  gradual  and  irregular  rise 
of  the  land.  The  forces  of  elevation  and  depression  have  acted  not  once  only 
but  many  times;  and  accordingly  the  whole  surface  of  the  land  has  been,  not 
once  only,  but  often,  subjected  to  the  grooving  tools  and  gouges,  the  planes 
and  chisels,  so  to  speak,  of  the  upper  surface  of  the  sea ;  the  hollows  and  ex- 
cavations thus  caused  not  having  been  obliterated,  but  generally  deepened 
and  intensified  on  each  occasion." 

153.  If  a  person  will  have  the  curiosity  to  lift  a  gallon  of  water  from  almost 
any  river  during  its  muddy  and  turbid  condition,  consequent  upon  floods, 
and  allow  it  to  settle,  he  will  be  astonished  at  the  amount  of  sediment  or 
solid  matter  that  falls  to  the  bottom.  Now,  let  him  multiply  this  gallon  by 
the  number  of  gallons  daily  carried  down  by  the  river,  and  this  day  by  years 
and  centuries,  and  he  will  arrive  at  some  faint  idea  of  the  quantity  of  matter 
worn  from  the  land  by  rivers  and  deposited  upon  the  bod  of  the  ocean. 

Some  of  the  results  of  observations  on  the  action  of  particular  rivers  are  as 
follows :  The  total  mineral  matter  carried  by  the  Ganges  into  the  sea  is  esti- 
mated at  upward  of  six  thousand  millions  cubic  feet  per  annum.  To  trans- 
port this  quantity,  says  Mr.  Lyell,  would  require  a  fleet  of  2,000  ships,  each  of 
1,400  tons,  to  start  every  day  throughout  the  year.  The  same  matter  would 
also  cover  a  square  space  eighteen  miles  on  the  side,  every  year,  with  mud  a 
foot  deep,  or  would  raise  a  surface  equal  to  one  half  the  area  of  all  the  New 
England  States  one  foot  in  the  space  of  144  years. 

The  Yellow  River  (Hoang  Ho),  in  China,  carries  down  into  the  Yellow 
Sea  43, 000, 000  of  cubic  feet  of  earth  daily;  so  that,  assuming  the  Yellow 
Soa  to  be  120  feet  deep,  an  English  square  mile  might  bo  converted  into  dry 
land  every  seventy  days. 

The  quantity  of  solid  matter  annually  brought  down  by  the  Mississippi,  and 
discharged  into  the  Gulf  of  Mexico,  has  been  estimated  to  exceed  three  thou- 
sand million  cubic  feet ;  and  that  transported  to  the  sea  by  oven  so  small  a 
liver  as  the  Merrimac,  in  Massachusetts,  at  840,000  tons. 

154.  Deltas, — When  the  matter  thus  carried  down  by 
rivers  is  deposited  at  their  mouths^  a  triangular  area  of 
land  is  added  to  the  previously  existing  shore — the  base 
of  the  triangle  extending  toward  the  open  water  and  the 
apex  being  up  the  stream.  Such  formations,  from  their 

QUESTIONS. — What  is  eaicl  of  the  amount  of  sediment  conveyed  by  rivers  to  the  ocean  ? 
What  is  the  estimated  amount  of  sediment  brought  down  by  some  of  the  rivers  of  Asia? 
What  by  the  Mississippi  ?  What  are  deltas  ? 


154        FIRST     PRINCIPLES     OF     GEOLOGY. 

resemblance  to  the  fourth  letter  of  the  Greek  alphabet  (A), 
are  termed  deltas,  and  they  generally  divide  the  main 
stream  into  several  branches. 

The  delta  of  the  Mississippi  includes  a  large  part  of  Lower  Louisiana,  and 
comprises  an  area  of  over  13,000  square  miles.  The  mean  depth  of  the 
deposit  of  sediment,  constituting  this  delta,  is  estimated  at  not  less  than  500 
feet,  and  the  formation,  at  the  present  time,  advances  steadily  out  into  the 
Gulf  of  Mexico  at  the  rate  of  about  one  mile  in  a  century,  or  fifty  feet  per 
annum.  The  delta  formed  by  the  Ganges  is  of  still  larger  dimensions.  It 
commences  220  miles  from  the  sea,  and  has  a  base  of  200  miles,  through 
which  extent  of  made  land  the  river  discharges  itself  by  eight  principal  chan- 
nels, and  an  almost  infinite  number  of  smaller  ones.  Fig.  90.  represents  the 
delta  of  the  Ganges,  with  its  numerous  channels. 

FIG.  90. 


The  gain  of  land  at  the  mouth  of  the  River  Po,  in  Italy,  has  been  so  great 
that  the  town  of  Adria,  which  was  a  seaport  in  the  time  of  Augustus,  and 
gave  its  name  to  the  adjacent  gulf  (Adriatic),  is  now  upward  of  twenty  miles 
inland. 

"Where,  however,  the  mouth  of  the  river  is  subjected  to  strong  tides,  or  is 
swept  by  powerful  oceanic  currents,  the  detritus  brought  down  does  not  form 
a  delta  but  is  carried  off  directly  into  the  sea,  as  in  the  case  of  the  Amazon, 
the  La  Plata,  St.  Lawrence,  and  most  of  the  rivers  of  Europe. 

Q-CESTIONS. — What  is  said  of  the  delta  of  the  Mississippi  ?  What  of  the  Ganges  ?  Do 
deltas  form  at  tlio  raoutha  of  all  rivers? 


AQUEOUS      AGENCIES. 


155 


155.  From  the  evidence  thus  presented  respecting  the  amount  of  mineral 
matter  carried  by  rivers  into  the  sea,  it  is  altogether  probable  that  accumu- 
lations are  now  forming  on  the  bed  of  the  ocean  on  as  large  a  scale  as  at 
any  former  period.  The  sedimentary  matter  thus  deposited,  moreover,  will 
take  the  form  of  strata,  as  the  amount  of  sediment  swept  into  the  ocean  from 
the  land  is  not  constant,  and  is  derived,  at  different  times,  in  larger  propor- 
tion from  some  districts  than  from  others.  Such  formation  would  include 
also  the  remains  of  man  and  his  productions,  and  of  land  and  marine  animals 
and  vegetables ;  so  that  if  the  bed  of  any  ocean,  as  that  of  the  Atlantic  along 
the  coast  of  the  United  States,  should  ever  be  elevated  and  converted  into 
dry  land,  the  future  geologists,  by  exploring  its  succession  of  strata  and  study- 
ing the  fossils  contained  in  them,  would  be  able  to  form  a  very  correct 
opinion  as  to  the  conditions  of  life  and  climate  that  prevailed  in  the  vicinity 
at  the  time  the  deposits  in  question  originated. 

156.  Waves,  Tides,  and  Oceanic  Currents  act  in  pro- 
ducing geological  changes  in  the  same  manner  as  streams 
and  rivers.  They  all  waste  and  wear  away  the  sea-coast 
in  exposed  districts,  and  deposit  the  abraded  material,  in 
the  form  of  mud,  sand,  gravel,  etc.,  in  other  localities. 

FIG.  91. 


The  abrading  power,  which  waves  are  capable  of  exerting  upon  any  par- 
ticular coast,  varies,  of  course,  with  their  own  magnitude,  as  well  as  with  the 
nature  and  position  of  the  rocks  exposed  to  their  action.  Mr.  Stevenson,  the 
celebrated  English  engineer,  proved,  by  experiment,  some  years  since,  that 
the  force  exerted  by  the  waves  of  the  German  ocean  during  a  storm,  in  favor- 
able situations,  was  about  one  and  a  half  tons  per  square  foot,  and  by  the 
waves  of  th3  Atlantic  three  tons. 

QUESTIONS. — Are  accumulations  probably  now  forming  in  the  ocean  of  great  extent? 
In  what  manner  do  waves,  tides,  and  currents  produce  geological  changes?  How  doea 
the  actionx>f  waves  on  coasts  vary  ?  What  ia  the  estimated  power  of  ocean  wavea  in  a 
storm? 


156      FIRST     PRINCIPLES     OF     GEOLOGY. 

A  coast-line,  consisting  of  soft  clays  and  sands,  will  suffer  more  waste  than 
one  composed  of  sandstones  and  shales,  and  these,  again,  will  yield  more 
readily  than  cliffs  of  basalt  and  granite.  Farther,  strata  that  dip  seaward, 
and  present,  breakwater  like,  their  natural  slopes  to  the  action  of  the  waves, 
as  in  Fig.  91,  will  suffer  less  than  those  whose  outcropping  ridges  are  presented 
to  the  storm,  as  in  Fig.  92. 

FIG.  92. 


It  occasionally  happens  (as  in  the  case  represented  in  Fig.  92)  that  the 
waste  produced  at  first  by  the  action  of  the  waves  accumulates  at  the  base 
of  a' cliff,  and  forms  a  natural  rampart  preventing  further  destruction.  It  is 
this  condition  that  is  frequently  imitated  by  engineers  when  they  desire  to 
prevent  further  encroachments  of  the  sea  on  an  exposed  coast. 

157.  Striking  examples  of  the  erosive  action  of  the  ocean  upon  the  land 
might  be  cited  almost  without  number.  Thus,  the  English  Channel  is  sup- 
posed to  have  been  excavated  by  the  ocean,  inasmuch  as  the  geological  fea- 
tures of  the  coasts  of  England  and  France  clearly  indicate  that  they  were 
formerly  united.  During  the  thirteenth  century,  a  strait,  half  as  wide  as  the 
English  Channel,  was  formed  in  less  than  100  years,  separating  Friesland 
from  the  north  of  Holland ;  and  islands  in  the  German  Ocean,  and  towns  and 
villages  upon  the  coast  of  England,  have  also  been  entirely  swept  away  by 
the  sea  within  the  historic  period. 

In  the  United  States,  the  bold,  rocky  coasts  of  New  England  in  particular, 
exhibit  abundant  evidence  of  the  abrading  power  of  the  ocean.  In  many 
localities  the  rocks  are  scooped  and  hollowed  into  the  most  irregular  shapes ; 
and  fragments,  which  once  constituted  part  of  the  mainland,  may  be  observed 
standing  detached  at  some  considerable  distance  from  the  shore.  (See  Fig. 
93.)  Boston  Harbor  has  evidently  been  formed  in  great  part  by  the  wasting 
agency  of  the  ocean ;  and  many  of  the  islands  in  it,  which  were  once  parts  of 
the  continent,  have  only  been  preserved  from  destruction,  during  the  last 
few  years,  by  artificial  embankments.  At  Cape  May,  on  the  north  side  of 
Delaware  Bay,  the  sea  has  encroached  upon  the  land  at  the  rate  of  about 
nine  feet  in  a  year ;  and  at  Sullivan's  Island,  in  Charleston  (S.  C.)  harbor,  it  has 
advanced  a  quarter  of  a  mile  in  three  years.  Great  accumulation  of  pebbles 
are  common  along  many  coasts,  and  seem  to  remain  stationary,  since  there 

QUESTIONS. — What  are  some  examples  of  the  erosive  action  of  the  waves  ia  Europe  ? 
What  are  examples  upon  our  own  coasts? 


AQUEOUS     AGENCIES. 


157 


are  always  piles  of  pebbles  to  be  found  in  the  same  places ;  but  if  these  are 
watched,  the  accumulations  will  be  found  to  consist  of  different  pebbles  from 
day  to  day,  each  pebble  being  in  turn  washed  from  its  place,  which  is  occu- 
pied by  another  like  it. 

158.  The  action  of  tides  and  oceanic  currents  is  chiefly  manifested  in  their 
power  of  transporting  and  assorting  the  debris  borne  into  the  ocean  by  rivers, 
or  produced  by  the  erosion  of  waves,  or  arising  from  the  growth  and  de- 
cay of  marine  animals  and  plants.  The  action  of  the  tide,  especially,  is  that 
of  constant  deposition,  and  is,  in  a  measure,  antagonistic  to  the  action  of 
waves  and  storms. 

FIG.  93. 


The  changes  produced  upon  our  own  coast  by  the  tides  are  not  only  geo- 
logically interesting,  but  of  the  utmost  importance  to  the  trade  and  naviga- 
tion of  the  country.  At  Sandy  Hook,  New  York  harbor,  for  example,  where 
there  is  now  dry  land,  there  were,  in  1836,  forty  feet  of  water.  In  1767, 
there  was  an  open  ship-channel  from  Barnstable  Bay,  Mass.,  to  the  ocean; 
but  the  deposits  of  the  tides  have  closed  up  the  opening  and  converted  it  into 
a  part  of  Cape  Cod.  A  considerable  number  of  harbors  and  inlets,  on  our 
coast,  particularly  along  Martha's  Vineyard  and  Long  Island,  have  been 
gradually  closed  by  tidal  action  and  converted  into  ponds,  and  in  the  course 
of  a  few  years  the  salt  water  in  them  gradually  gives  place  to  fresh  water. 
In  some  cases  the  bottom  of  these  ponds  is  deeper  than  the  bottom  of  the 
adjoining  ocean.* 

QUESTIONS. — What  is  said  of  the  action  of  tides  and  currents?  Is  the  influence  of  the 
tides  the  same  as  that  of  waves?  What  are  some  examples  of  tidal  action  on  our  own 
coast  ?  

*  This  fact  is  one  of  interest,  since  it  is  found  that  the  inhabited  parts  of  sandy  deserts, 
such  as  the  oases  of  the  Desert  of  Sahara,  present  similar  depressions,  the  bottom  of  the 
valley  being,  in  some  instances,  below  the  level  of  the  sea.  During  the  changes  in  tho 


158        FIRST      PRINCIPLES      OF      GEOLOGY. 

Captain  Davis,  U.S.IT.,  as  the  result  of  bis  investigations,  thinks  it  probable 
that  a  great  part  of  Long  Island  has  been  formed  of  materials  accumulated 
by  the  action  of  the  tides. 

159.  Marine  currents  may  be  regarded  as  great  oceanic  rivers.  Their 
transporting  power  is,  however,  greater  than  that  of  terrestrial  rivers,  since 
the  specific  gravity,  or  sustaining  power  of  sea-water  is  greater  than  that  of 
fresh  water.  They  also  possess  an  advantage  over  rivers,  in  transporting 
small,  light  particles  of  matter,  by  reason  of  their  greater  depth.  Thus,  it 
has  been  found,  by  experiment,  that  ordinary  river  sediment,  mechanically 
suspended  in  water,  settles  at  the  rate  of  about  one  foot  per  hour.  A  current, 
therefore,  500  feet  deep,  and  moving  at  the  rate  of  three  miles  per  hour, 
would  carry  its  sediment  1.500  miles  before  depositing  it.  Hence,  great  de- 
posits of  mud  may  be  in  the  course  of  formation  at  the  bottom  of  the  open 
sea,  even  when  the  surface  water  is  perfectly  clear. 

Currents  in  the  ocean  are  of  two  kinds,  drift  and  stream  currents.  The 
former  result  mainly  from  the  action  of  winds  and  tides,  and  are  of  no  great 
length  or  velocity.  The  latter  are  of  great  length,  depth,  and  velocity,  and 
are  caused  by  the  tendency  of  water,  displaced  in  the  ocean  by  excessive 
evaporation  in  the  tropics,  by  the  rotation  of  the  earth,  and  by  other  causes, 
to  maintain  an  equilibrium. 

The  number  of  these  great  ocean  rivers  is  very  large.  One  of  the  most 
powerful  and  extensive  is  the  so-called  "Gulf  Stream,"  which,  commencing 
in  the  Gulf  of  Mexico,  flows  in  a  northeasterly  direction  along  the  whole 
coast  of  the  United  States,  expanding  in  volume  and  diminishing  in  rapidity. 
On  striking  the  Banks  of  Newfoundland,  it  sets  to  the  east,  and  extends  to 
the  coasts  of  Europe  and  Africa.  Its  length,  from  Florida  to  the  Azores,  is 
3,500  miles,  which  is  traversed  in  seventy-eight  days,  at  an  average  rate  of 
thirty-eight  miles  per  day.  The  amount  of  water  conveyed  in  it  is  more  than 
3,000  times  the  amount  discharged  by  the  Mississippi  Elver — many  times 
greater  than  all 'the  fresh  water  in  the  rivers  of  the  globe.  In  a  part  of  its 
course,  near  the  Florida  Gulf,  its  velocity  is  that  of  a  torrent — five  miles  per 
hour.  Mr.  Lyell  thinks  it  not.  improbable  that  some  of  the  sediment  brought 
down  by  the  Mississippi  may  bo  conveyed  by  the  Gulf  Stream  as  far  as  the 
Banks  of  Newfoundland,  before  it  is  deposited.  • 

Another  similar  great   current  exists  in  the  Pacific,  and  less  extensive 

QUESTIONS.— How  may  marine  currents  be  regarded  ?  What  is  said  of  their  trans- 
porting power  ?  What  two  kinds  of  currents  exist  in  the  ocean?  How  do  "drift"  cur- 
rents originate  V  How  do  "stream"  currents?  What  is  one  of  the  most  remarkable 
ocean  currents?  Describe  the  course,  length,  and  velocity  of  the  Gulf  Stream.  How 
far  is  the  Gulf  Stream  supposed  to  convey  sediment  ? 


formation  of  these  ponds  they  become  the  home,  in  succession,  of  salt  water  animals, 
brackish  water  animals,  and  fresh  water  animals,  thus  affording  a  beautiful  demonstra- 
tion of  the  geological  formation  of  basins,  such  as  those  of  London  and  Paris,  in  which 
the  remains  of  successive  races  of  animals  are  found  in  a  fossil  state. — Capt.  Davis. — 
SmitJiaonian  Publications. 


AQUEOUS     AGENCIES. 


159 


ones  in  all  the  great  divisions  of  the  different  oceans.  All  these  must,  in 
some  places,  be  wearing  down  the  bed  of  the  ocean,  producing  indentations 
and  irregularities  in  its  coast  lines,  and  accumulating  in  other  localities  an 
immense  amount  of  detrital  matter  for  the  formation  of  now  strata. 

1GO.  Ancient  Erosive  Action  of  the  Ocean, — "As  actual  sea- 
cliffs  are  proofs  of  the  erosive  action  of  the  sea  now  in  operation,  so,  in  almost 
all  cases,  inland  cliffs,  crags,  scars,  and  precipices,  as  well  as  valleys,  ravines, 
gorges,  and  mountain  passes,  are  proofs  of  the  former  erosive  action  of  the 
sea,  in  times  when  the  land  stood  at  a  lower  level  in  respect  to  it ;  and  the 
dimensions  of  the  gaps  and  portions  removed,  combined  with  the  strength 
and  durability  of  the  materials,  give  us  a  measure  of  the  power  of  the  erod- 
ing forces,  and  the  time  during  which  they  were  in  action."  Another  won- 
derful example  of  this  agency  is  to  be  found  in  the  immense  accumulations 
of  water-worn  materials,  i.  e.t  gravel,  sand,  and  clay,  which  cover  great  areas 
of  the  surface  of  the  earth  to  a  depth,  in  some  places,  of  hundreds  of  feet. 
No  one  who  thinks  for  a  moment  over  a  rounded  pebble  can  doubt  that 
it  was  once  a  part  of  a  continuous  rock,  and  that  it  has  assumed  its  present 
state  through  mechanical  action ;  and  the  same  conclusion  is  also  applicable 
to  every  particle  of  sand  and  clay.  Of  the  conditions  of  time  and  power 
requisite  for  the  production  of  such  effects,  the  mind,  can  form  but  a  faint 
conception. 

FiG.  94. 


In  some  districts  of  country,  however,  the  position  of  strata  furnishes  us  with 
very  reliable  data  for  estimating  the  amount  of  rock  which  has  at  a  former 
period  been  utterly  destroyed  and  swept  away  by  the  erosive  action  of  water. 
Thus,  in  cases  like  that  shown  in  Fig.  94,  no  one  can  doubt  that  the  valley 
at  B  was  once  filled  with  rock,  since  the  position  of  the  strata  on  both  sides 
indicate  that  they  were  once  continuous,  as  they  still  are  below  the  bed  of 
valley.  In  other  cases,  as  at  A  and  (7,  the  inclination  of  the  strata  shows 
not  only  that  a  valley  has  been  excavated,  but  that  an  entire  mountain, 
which  formerly  existed,  has  been  swept  off. 

Measurements  of  this  kind  have  enabled  Professor  Hitchcock  to  prove,  that 
in  some  parts  of  the  Yalley  of  the  Connecticut,  nearly  10,000  feet  in  vertical 

QUESTIONS. — What  is  said  of  the  ancient  erosive  action  of  the  ocean  ?  What  inference 
may  we  draw  from  accumulations  of  sand  and  gravel  ?  Show  how  we  can,  in  certain 
cases,  approximately  estimate  the  amount  of  erosion  by  water. 


160        FIRST     PRINCIPLES     OF     GEOLOGY. 

thickness  of  rock  has  been  removed;  or,  in  other  words,  that  the  country  ha 
some  localities  was  once  nearly  two  miles  higher  than  it  is  at  present. 

161.  "In  considering  the  destructive  action  of  water,  however,  we  must 
never  forget  that  by  destruction  we  do  not  mean  annihilation  but  only  re- 
arrangement. Rock-forming  land,  that  is,  rock  above  the  level  of  the  sea,  is 
destroyed,  but  its  materials  are  carried  off  and  deposited,  either  in  similar  or 
different  combinations,  to  form  rock  below  the  level  of  the  sea." 


SECTION     III. 

ORGANIC      AGENCIES. 

162.  The  organic  agencies  tending  to  produce  geologi- 
cal changes  are  those  depending  on  animal  and  vegetable 
growth. 

163.  Vegetable  Action^ — The  growth  and  decay  of  vegetables  are 
yearly  adding  to  the  soil,  and  at  the  same  time  they  protect  the  surface  from 
the  wasting  action  of  rain,  frost,  and  the  like.  One  of  the  great  aids  to  rapid 
disintegration  in  Arctic  countries,  and  in  high  mountain  districts,  is  the 
absence  of  a  superficial  covering  of  vegetation — a  covering  which,  on  the 
other  hand,  protects  the  tropical  soil  from  the  wasting  effects  of  the  heavy 
rains  which  fall  periodically  in  these  latitudes. 

Peat , — In  most  of  the  swamps  of  the  temperate  zones  deposits  of  vege- 
table growth,  known  as  peat,  are  constantly  accumulating.  This  substance 
is  formed  principally  by  the  decay  of  the  fibrous  roots  of  mosses,  especially 
of  those  varieties  which  continually  throw  up  new  shoots  from  the  decaying 
extremities  below.  "When  perfectly  formed,  peat  does  not  exhibit  a  fibrous 
structure,  and,  when  wet,  has  the  appearance  of  a  fine  black  mud.  Dry  peat 
contains  from  sixty  to  ninety-five  per  cent,  of  carbonaceous  matter,  and  in 
this  condition  constitutes  a  valuable  fuel.  Deposits  of  peat  are,  in  some  in- 
stances, from  thirty  to  forty  feet  in  thickness,  and  may  extend  over  consider- 
able areas  of  the  earth's  surface.  A  peat  "moss,"  or  bog,  on  the  River 
Shannon,  in  Ireland,  covers  an  area  of  150  square  miles.  In  tropical  coun- 
tries peat  is  rarely  formed,  on  account  of  the  too  rapid  decomposition  of  the 
vegetable  matter. 

Great  accumulations  of  vegetable  matter  also  result  from  the  waste  and 
decay  of  forests,  jungles,  and  cypress  swamps,  and  from  vegetable  drift  of 
rivers.  On  a  branch  of  the  Mississippi — the  Atchafalaya — in  Louisiana,  the 
quantity  of  drift  and  water-logged  timber  that  accumulated  in  thirty-five 

QUESTIONS. — What  fact  must  be  taken  into  consideration  in  estimating  the  destruc- 
tive action  of  water?  What  are  the  organic  agencies  tending  to  produce  geological 
changes  ?  What-is  said  of  vegetable  action  ?  What  is  peat  ?  What  is  said  of  the  loca- 
tion and  extent  of  peat-bogs  ?  "What  of  vegetable  drift  of  rivers  ? 


ORGANIC     AGENCIES.  161 

years  was  Bufficient  to  form  a  raft  ten  miles  long,  220  yards  wide,  and  eight 
feet  deep.  The  whole  rose  and  fell  with  the  water,  and  yet  became  covered 
with  growing  vegetation,  and  of  course  with  soil.  This  raft  went  on  increas- 
ing until  about  1835,  when  some  of  the  trees  upon  it  had  grown  to  the  height 
of  sixty  feet.  Steps  were  then  taken,  by  the  State  of  Louisiana,  to  clear  it 
away  and  open  navigation,  which  was  effected,  with  great  labor  and  expense, 
in  the  space  of  four  years.  Similar  rafts  are  now  in  existence  upon  the  Red, 
the  Washita,  and  other  rivers  flowing  into  the  Gulf  of  Mexico. 

The  prodigious  quantity  of  wood  drifted  down  by  the  Mississippi  and  other 
large  rivers,  which  pass  through  heavily  timbered  regions,  is  a  subject  of 
great  geological  interest,  since  it  illustrates  the  manner  in  which  an  abundance 
of  vegetable  matter  becomes,  in  the  ordinary  course  of  nature,  imbedded  in 
sub-aqueous  deposits.  Thus,  a  part  of  this  wood  is  carried  into  the  main 
ocean,  and  conveyed  by  currents  to  remote  latitudes.  Some  of  the  timber, 
for  example,  that  comes  down  the  Mississippi,  is  believed  to  be  transported 
by  the  Gulf  Stream  as  far  as  the  shores  of  Greenland  or  Norway.  The 
greater  portion,  however,  collects  in  eddies  or  on  bars  along  the  shores,  and 
after  a  time  becomes  saturated  with  water  and  sinks  to  the  bottom.  The  de- 
posit thus  formed  becomes  covered  with  mud,  and  this  in  turn  is  overlaid 
with  other  layers  of  drift  wood  and  sediment ;  and  thus,  in  the  course  of  time, 
successive  strata  of  nearly  pure  vegetable  matter  and  earthy  sediment  are  ac- 
cumulated. 

It  is  found,  in  excavating  at  New  Orleans,  that  the  soil  (which  is  a  part  of 
the  delta  of  the  Mississippi),  to  a  depth  considerably  below  the  level  of  the 
sea,  contains  innumerable  trunks  of  trees,  layer  above  layer ;  some  prostrate, 
as  if  drifted,  others  remaining  still  erect,  and  with  their  roots  spreading  on 
all  sides,  as  if  in  their  natural  position. 

Coal,  as  will  be  hereafter  shown,  is  but  a  mass  of  mineralized  vegetation, 
and  under  favorable  conditions  all  the  various  vegetable  accumulations  above 
described  would  constitute  similar  mineralized  deposits. 

Action  of  Animals  . — The  mode  in  which  animals  tend  to  affect  the 
crust  of  the  earth  is  chiefly  by  adding  their  waste  secretions  or  coverings.. 
It  is  true  that  the  bones  and  other  remains  of  the  larger  animals  are  often 
buried  in  the  mud  of  lakes  and  rivers,  there,  in  time,  to  form  solid  petrifac- 
tions, and  leave  records  of  the  past  life  of  the  globe ;  but  such  an  effect  is 
trifling  compared  with  the  accumulations  of  shells,  infusorial  remains,  and  the 
productions  of  coral  animals.  Many  mollusks,  as  oysters,  clams,  and  muscles, 
live  in  beds  of  considerable  thickness,  and  if  buried  in  sediment  on  the  bottom 
of  the  ocean,  will,  in  time,  form  layers  of  shelly  limestone,  like  those  occur- 
ring among  the  strata  formed  in  past  ages  of  the  world.  On  many  coasts 
we  also  find  thick  accumulations  of  drifted  shells ;  and  the  marl,  or  whitish 

QUESTIONS.— What  are  remarkable  illustrations  of  river  drift  ?  Illustrate  the  manner 
in  which  vegetable  matter  may  become  imbedded  in  strata?  How  do  animals  affect  the 
crust  of  the  earth  ?  Illustrate  this  ?  What  organic  agent  is  most  influential  in  producing 
geological  changes? 


162 


FIRST     PRINCIPLES     OF     GEOLOGY. 


mud,  which  constitutes  the  bottom  of  many  fresh-water  lakes,  is  often  almost 
wholly  composed  of  fresh- water  shells  and  the  remains  of  infusoria. 

164.  Corals, — But  the  most  important  and  wonderful 
exhibition  of  organic  agency  in  modifying  the  crust  of  the 
earth  is  found  in  the  operations  of  the  coral  polyps. 

Endowed  with  the  power  of  secreting  lime  from  the  waters  of  the  ocean, 
these  minute  animals  construct  banks  or  reefs  of  coral  rock  around  every 
island  and  shore  of  the  tropical  oceans,  where  conditions  of  depth  and  cur- 
rent are  favorable  to  their  development.  Many  of  these  reefs,  in  the  Pacific 
and  Indian  Oceans,  extend  for  hundreds  of  miles,  and  are  of  great  breadth 
and  thickness.  Thus,  on  the  northeast  coast  of  Australia,  a  coral  reef  exists, 
which  is  more  than  1,000  miles  in  length,  from  ten  to  ninety  in  breadth,  and 

95. 


in  some  places  rises,  at  its  seaward  edge,  from  depths  of  at  least  1,800  feet. 
This  reef  is  parallel  with  the  shore,  but  at  a  considerable  distance  from  it, 
i.  e.,  from  twenty  to  sixty  miles.  Another  reef,  along  the  island  of  New 
Caledonia,  is  400  miles  long ;  and  many  others  in  the  Pacific  have  a  nearly 
equal  extension.  In  fact,  "the  absolute  area  of  sea-bottom,  in  this  ocean, 
thus  occupied  at  intervals  by  the  work  of  the  coral  animals,  is  so  enormous, 
that  it  would  be  difficult  to  parallel  it  by  reference  to  any  existing  mountain 
district." 

QUESTIONS.— What  is  the  nature  of  the  action  of  the  coral  animals  ?    What  is  said  of 
the  extent  of  their  operations? 


ORGANIC     AGENCIES.  163 

"  The  animals  which  produce  coral  are  very  simple,  and  resemble  plants, 
both  in  their  figures  and  colors.  Indeed,  they  were  formerly  described  as 
marine  plants.  They  vary  in  size  from  a  minute  fraction  of  an  inch  to  several 
inches  in  diameter ;  and  live  either  solitary  or  associated  in  immense  num- 
bers. From  their  resemblance  to  plants,  the  coral  animals,  as  a  class,  are 
often  called  'zoophytes.' 

"  The  coral  secreted  by  the  polyps  is  not  a  collection  of  cells  in  which  the 
animals  may  conceal  themselves,  but  an  internal  skeleton ;  nor  do  they  ex- 
hibit any  industry  or  instinct  in  forming  it,  but  it  results  from  vital  processes  in 
their  system,  which  they  no  more  control  than  do  the  more  highly  organized 
animals  the  formation  of  their  bones.  Every  part  of  live  coral  also  is  wholly 
enveloped  by  the  texture  of  the  polyps  which  produced  it."  Figs.  95,  106, 
and  147,  represents  some  of  the  varieties  of  coral. 

The  coral  polyps  increase  mainly  by  buds,  which  shoot  out  from  their  sides 
in  a  manner  similar  to  the  buds  of  plants.  On  coral  formations  these  buds 
spread  out  so  thickly  as  to  stop  the  life  within ;  and  hence,  as  the  process 
goes  on,  all  is  a  dead  mass  except  just  at  the  surface.  The  reef-building 
corals  are  furthermore  limited  in  their  range  of  depth,  and  operate  only 
where  perpetually  covered  by  the  tides  and  downward  to  the  extent  of 
120  to  180  feet. 

FiG.  96. 


The  growth  of  coral  structures  is  extremely  slow,  and  the  rate  of  increase 
has  been  estimated  to  be  about  a  half  an  inch  per  annum.  The  seas,  how- 
ever, in  which  corals  occur,  abound  also  with  shells  and  other  marine  ani- 
mals, which  by  their  remains  contribute  greatly  to  augment  the  mass  of  the 
coral  formation. 

Three  classes  of  coral  reefs  are  recognized :  First,  "fringing  reefs,"  or  belts 
of  coral  attached  to  the  coasts  of  islands  or  continents ; 

Second,  "barrier  reefs,"  which  form  rising  walls  at  some  distance  from  the 
land,  and  between  which  and  the  land  a  broad,  safe  channel  frequently  exists. 

QUESTIONS.— What  is  said  of  the  structure  of  the  coral  animals?  What  relation  does 
the  coral  rock  sustain  to  the  organism  that  produces  it?  Do  the  coral  animals  work  in  all 
depths  of  water  ?  How  fast  does  coral  increase  ?  How  many  classes  of  coral  reefs  are 
recognized ?  What  are  fringing  reefs?  What  are  barrier  reefs ? 


164         FIBST     PRINCIPLES     OF     GEOLOGY. 

Such  reefs  are,  in  some  instances,  ninety  miles  in  diameter.  On  the  ocean 
side  they  terminate  abruptly  in  deep  water,  but  within,  the  slope  is  gradual. 
Tig.  96  represents  a  barrier  reef  encircling  the  island  of  Bolabola,  in  the 
Pacific ;  it  will  be  observed  to  be  entirely  separated  from  the  island  and 
covered  with  trees ; 

FIG.  97. 


Third,  encircling  reefs,  or  "  afoZs,"  as  they  are  called.  These  are  the  most 
common  form  of  coral  islands  found  in  the  Pacific.  The  diameter  of  these 
encircling  reefs  varies  from  one  to  forty  miles,  and  their  breadth  from  a  few 
yards  to  more  than  a  mile.  They  inclose  a  space  of  quiet  waters,  called  a 
lagoon,  which  generally  communicates  with  the  ocean  by  one  or  more  open- 
ings through  the  reef.  Fig.  9T  represents  an  "atol"  of  the  Pacific,  known 
as  "Whit-Sunday  Island.*  «f  .1  \ 

QUESTION. — "What  are  the  characteristics  of  the  circular  reefs? 

*  "  The  appearance  of  these  coral  islands  is  extremely  picturesque.  A  small  ring  of 
land,  of  circular  or  oval  shape,  and  a  few  hundred  yards  across,  rises  barely  above  high 
water-mark,  and  is  fringed  with  mangroves  and  often  dotted  with  cocoa-nut  palms.  Be- 
tween these  and  the  water  is  a  beach  of  glittering  white  sand,  the  outer  margin  of  which 
is  encircled  by  another  ring  of  snow-white  breakers,  beyond  which  again  are  the  dark 
heaving  waters  of  the  open  ocean.  The  inner  beach  incloses  the  calm,  clear  water  of 
the  lagoon,  resting,  for  the  most  part,  on  white  sand,  and  showing  the  most  vivid  green 
color  when  the  sun  is  shining." 

"The  ocean,"  says  Mr.  Darwin,  "throwing  its  breakers  on  the  outer  shore,  appears 
an  invincible  enemy,  yet  we  see  it  resisted,  and  even  conquered,  by  means  which  at  first 
seem  weak  and  inefficient.  No  periods  of  repose  are  granted,  and  the  heavy  swell  caused 
by  the  steady  action  of  the  trade  wind  never  ceases.  The  breakers  exceed  in  violence 
those  of  our  temperate  regions ;  and  it  is  impossible  to  behold  them  without  feeling  a 
conviction  that  rocks  of  granite  or  quartz  would  ultimately  be  demolished  by  such  ir- 
resistible forces.  Yet  these  low  coral  islands  stand  and  are  victorious,  for  here  another 
power,  antagonistic  to  the  former,  takes  part  in  the  contest.  The  organic  forces  separate 
the  atoms  of  carbonate  of  lime,  one  by  one,  from  the  foaming  breakers,  and  unite  them 
into  a  symmetrical  structure ;  myriads  of  architects  are  at  work  day  and  night,  month 
after  month,  and  we  see  their  soft  and  gelatinous  bodies,  through  the  agency  of  the  vital 
laws,  conquering  the  great  mechanical  power  of  the  waves  of  the  ocean,  which  neither  the 
art  of  man  nor  the  mechanical  works  of  nature  could  successfully  resist." 


ORGANIC     AGENCIES.  165 

Coral  reefs,  as  has  been  stated,  consist  of  living  corals  only  at  their  upper 
and  outer  surface ;  all  the  interior  is  composed  of  dead  corals  and  shells, 
either  whole  or  in  fragments,  and  the  calcareous  portions  of  other  marine 
animals.  The  interstices  of  the  mass  are  filled  up  and  compacted  together 
by  calcareous  sand  and  mud,  derived  from  the  waste  and  debris,  the  wear 
and  tear  of  the  corals  and  shells,  and  by  countless  myriads  of  minute  organ- 
isms, mostly  calcareous  also.  The  surface  of  a  reef,  where  exposed  at  low 
water,  is  composed  of  a  solid-looking  stone,  which  is  often  capable  of  being 
split  up  and  lifted  in  slabs,  bearing  no  small  resemblance  to  some  of  our  old- 
est limestones.  These  slabs  and  blocks,  when  broken  open,  are  frequently 
found  to  have  a  semi-crystalline  structure  internally,  by  which  the  forms  and 
the  organic  structure  of  the  corals  and  shells  are  more  or  less  disguised  or 
obliterated. 

"When  a  growing  reef  has  reached  the  level  of  low  water,  the  growth  of 
coral  ceases,  and  loose  materials  begin  to  accumulate  upon  its  summit. 
Large  blocks  of  coral  are  thrown  up  by  the  waves  and  gradually  ground  into 
calcareous  sand  and  gravel ;  sea-weeds  and  wood  are  washed  up,  and  upon 
the  soil  thus  formed  vegetation  commences,  and  the  reef  finally  becomes  a 
habitable  island.  This  action,  on  our  own  coast,  is  strikingly  illustrated  in 
Florida,  the  southern  portion  of  which  State,  according  to  Professor  Agassiz, 
"is  only  a  vast  coral  bank  composed  of  a  series  of  reefs,  which  have  success- 
ively grown  up  from  the  bottom  of  the  sea  to  the  surface,  and  have  been 
added  to  the  main-land  by  the  gradual  filling  up  of  the  intervals  which  sepa- 
rate them,  with  deposits  of  coralline  sand  and  debris,  brought  thither  by  the 
action  of  tides  and  currents.  On  the  solid  reefs,  the  action  of  the  waves  ac- 
cumulates mud  and  sand  to  a  height  of  twelve  feet  above  the  sea-level ;  and 
this  soil  becomes  rapidly  fixed,  by  the  growth  of  mangrove  trees  and  other 
plants.  The  intervals  being  lower,  form  large  fresh-water  swamps,  filled 
with  many  kinds  of  aquatic  plants,  through  which  the  Indian  can  only  pene- 
trate with  a  boat.  The  higher  and  drier  reefs  are  the  so-called  '  Hummocks,' 
which  rise  like  islands  from  the  deep  green  swamps  that  bear  the  name  of 
'Everglades.'  This  formation  is  still  in  progress,  and  the  so-called  'Keys' 
which  border  the  Florida  coast,  are  only  a  new  line  of  hummocks,  which  will 
eventually  be  added  to  the  mainland  by  everglades  formed  by  the  deposits 
of  the  sea." 

The  peculiar  form  of  the  coral  islands  and  reefs  of  the  Pacific,  and  the 
great  depths  from  which  they  rise,  has  been  the  subject  of  much  speculation 
among  geologists,  since,  as  has  been  already  stated,  the  coral  animal  does  not 
live  in  very  deep  water.  The  explanation  of  these  phenomena  most  generally 
accepted,  is,  that  the  coral  is  reared  upon  a  foundation  which  has  gradually 
subsided,  and  as  the  depression  has  gone  o^  slowly,  the  coral  has  continued 

QUESTIONS.— Describe  the  structure  of  a  coral  reef.  When  a  growing  reef  has  reached 
the  surface  of  the  water,  what  takes  place  ?  What  striking  illustration  of  the  action  of 
the  coral  animals  as  found  in  our  own  coast?  Describe  the  formation  of  the  Florida 
everglades  ?  To  what  is  the  peculiar  form  of  the  coral  islands  and  reefs  of  the  Pacific 
attributed  ?  Illustrate  how  the  circular  coral  islands  are  supposed  to  be  formed. 


166       FIRST     PRINCIPLES     OF     GEOLOGY. 

to  grow  to  a  corresponding  extent  upward.  On  such  a  supposition,  the  cir- 
cular coral  islands  (as  represented  in  Fig.  97)  would  indicate  the  position  of 
a  former  mountain,  around  which  the  coral  has  formed  a  fringe  or  reef.  As 
the  mountain  continued  to  sink,  the  reef  would  draw  inward  around  the  sum- 
mit, and  finally,  as  the  summit  went  under,  the  reef  would  still  remain  a  ring, 
with  a  lake  or  lagoon  in  the  center — for  the  polyps  could  not  work  in  the  middle 
till  the  whole  was  submerged,  and  even  then,  these  animals  prefer  the  open 
sea.  The  depth  of  water  in  the  immediate  proximity  of  such  islands,  is,  as 
might  have  been  expected,  almost  unfathomable.  Thus,  in  one  instance, 
noticed  by  Mr.  Dana,  in  the  geology  of  the  U.  S.  Exploring  Expedition, 
the  sounding  line,  within  three  quarters  of  a  mile  of  the  shore,  ran  out,  first 
2,000  feet;  then  at  a  short  distance  further  off1,  3,000  feet;  and  at  seven  miles 
from  the  shore,  no  bottom  was  found  at  6,800  feet.  At  Keeling  Island, 
another  coral  island  of  the  Pacific,  no  bottom  was  found  with  a  line  7,200 
feet,  at  a  distance  of  only  2,200  yards  from  the  shore. 

The  study  of  the  action  of  the  coral  animals  in  existing  oceans  prepares 
the  mind  of  the  geologist  for  the  investigation  of  operations  of  a  similar  char- 
acter, which  have  taken  place  in  the  seas  of  former  periods  of  the  earth's 
history.  Many  of  the  limestone  rocks,  which  now  form  portions  of  the  dry 
land,  are  undoubtedly  ancient  coral  reefs,  which  appear  to  have  been  formed 
under  conditions  analogous  to  those  which  now  prevail  in  the  waters  of  the 
Pacific. 


SECTION    IY. 

CHEMICAL      AGENCIES. 

The  changes  in  the  structure  of  the  earth's  crust,  re- 
sulting from  chemical  agencies,  are  numerous  and  compli- 
cated. 

They  have,  however,  been  noticed,  for  the  most  part,  in  previous  sections. 
Thus,  the  formation  and  deposition  of  travertine  and  calcareous  tufa,  stalac- 
tite, and  stalagmite,  silicious  sinter,  bog-iron  ore,  hydrate  of  manganese, 
gypsum,  rock-salt,  and  the  cementation  of  various  sands  into  compact  rocks, 
are  all  the  result  of  chemical  action.  Many  of  the  phenomena  connected 
with  volcanoes  and  earthquakes  may  also  be  referred  to  a  similar  origin. 

In  addition  to  these  results,  which  especially  appear  at  the  earth's  surface, 
chemical  forces,  called  into  activity  by  the  agency  of  heat,  water,  electric  and 
magnetic  currents,  are  continually  operating  hi  the  interior  of  the  earth's 
crust  to  produce  changes  or  metamorphism  in  the  structure  of  existing  rocks, 

QUESTIONS. — What  facts  tend  to  confirm  this  theory  ?  "Why  is  the  study  of  coral  growth 
of  peculiar  interest  to  geologists  ?  What  is  said  of  the  changes  in  the  earth's  crust  effected 
through  chemical  agencies?  What  are  eorae  illustrations  of  this  action  on  the  earth's 
surface? 


CLASSIFICATION     OF     ROCKS.  167 

viz.,  hardening  and  consolidating  some  strata,  softening  and  dissolving  away 
others,  filling  fissures  with  metallic  ores,  and  elaborating  new  compounds  by 
the  union  of  different  substances. 

M.  Bischoff,  a  German  chemist,  who  has  made  chemical  geology  "a  special 
study,  asserts  that  all  rocks,  through  the  action  of  chemical  forces,  are  con- 
tinually subject  to  alteration,  and  that  their  sound  appearance  is  no  indica- 
tion that  alteration  has  not  taken  place  in  them."  A  detailed  discussion  of 
these  subjects,  however,  presupposes  a  somewhat  extensive  acquaintance  with 
the  facts  of  terrestrial  chemistry,  and  would  be  foreign  to  the  plan  of  the 
present  work. 


CHAPTER    IX. 

CLASSIFICATION    OP    THE    MATERIALS    COMPOSING    THE 
EARTH'S  CRUST  INTO  PERIODS,  SYSTEMS,  AND  GROUPS. 

165.  To  a  mere  casual  observer,  the  different  mineral  or  earthy  materials 
constituting  the  crust  of  the  globe  must  appear  to  be  thrown  together  con- 
fusedly and  without  order.     Such,  however,  is  not  the  case ;  but  all  the  vari- 
ous rock-formations  have  been  found  capable  of  arrangement  into  divisions  or 
classes,  which  occupy  definite  positions  in  the  earth's  crust,  and  have  un- 
doubtedly been  formed  at  different  epochs  of  the  earth's  history. 

The  fundamental  idea  involved  in  every  system  of 
classification  of  rocks,  is  that  of  relative  age. 

This,  in  the  case  of  the  stratified  rocks,  may  be  determ- 
ined :  first,  by  the  relative  position  of  strata  ;  second,  by 
differences  in  mineral  composition ;  and,  third,  by  dif- 
ferences observed  in  the  nature  of  the  imbedded  fossils,  if 
any  such  are  present. 

166.  It  is  evident,  in  the  first  instance,  that  the  various  layers,  beds,  or 
strata  constituting  the  crust  of  the  earth,  are  the  result  of  a  succession  of 
operations,  all  requiring  time ;   and  that  in  every  case,  except  where  beds 
have  been  inverted  by  violence,  the  lowest  in  position  of  a  series  of  strata 
must  be  the  oldest,  while  the  other  superimposed  layers  must  have  been 
subsequently  formed,  in  the  order  of  their  upward  succession. 

QUESTIONS. — Do  changes  through  chemical  action  take  place  in  the  interior  of  the 
earth  ?  Do  the  earthy  materials  composing  the  crust  of  our  glohe  occur  confusedly  and 
without  order  ?  What  is  the  fundamental  idea  involved  in  every  system  of  classification 
of  rocks?  How  may  the  relative  age  of  the  stratified  rocks  be  determined  ?  How  does 
the  position  of  strata  indicate  their  age  ? 


168       FIRST     PRINCIPLES     OF      GEOLOGY. 

If  the  various  layers  of  stratified  rocks  extended  uniformly  over  the  whole 
globe,  and  had  never  been  disturbed  or  broken,  they  -would  inclose  one 
another,  and  envelop  the  earth  in  a  manner  similar  to  the  concentric  coats 
of  an  onion;  and  the  determination  of  the  relative  age  of  all  the  strata  could 
be  accurately  ascertained  by  simply  determining  their  relative  position. 
There  is,  however,  no  place  on  the  globe  where  any  such  uniformity  prevails, 
or  where,  if  a  section  was  made  sufficiently  deep  into  the  earth,  all  the  vari- 
ous rocks  would  be  found  superimposed  in  order  upon  each  other. 

The  reason  of  this  is  not  difficult  to  comprehend,  since,  as  changes  in  the 
distribution  of  land  and  water  are  known  to  have  occurred  at  every  epoch 
of  the  earth's  history,  particular  portions  of  its  surface  must  have  been  suc- 
cessively dry  land  and  sea-bottom  ;*  and  as  the  stratified  rocks  have  been 
formed  by  the  deposition  of  sediment  in  water,  it  is  obvious  that  those  por- 
tions of  the  globe,  which  constituted  dry  land  during  the  formation  of  a  de- 
posit in  a  surrounding  ocean,  could  have  received  no  portion  of  such  deposit, 
and  therefore  we  find,  as  might  naturally  be  expected,  that  certain  varieties 
of  rocks  are  restricted  to  particular  localities. 

16t.  Differences  in  mineral  composition  may  also  aid  in  determining  the  rela- 
tive ago  of  rocks,  inasmuch  as  some  mineral  substances  have  been  deposited 
more  abundantly  at  certain  periods  than  at  others.  Thus,  the  occurrence  of 
extensive  beds  of  chalk  characterizes  and  gives  name  to  a  system  of  rocks, 
known  as  the  "cretaceous"  or  "chalk"  formation;  while  beds  of  rock-salt 
and  of  coal  are  usually  found  associated  with  other  rocks  of  a  distinctive  and 
peculiar  character.  If  rocks,  moreover,  belonging  to  one  formation  are  found 
to  contain  imbedded  fragments  of  another  formation,  the  evidence  is  con- 
clusive that  the  rocks  to  which  the  fragments  belonged  were  formed,  con- 
solidated and  broken  up,  before  the  others  were  deposited. 

168.  The  evidence,  however,  upon  which  geologists  mainly  rely  for  de- 
termining the  relative  age  of  rocks,  is  the  character  of  the  organic  remains, 
or  fossils  imbedded  in  them.  An  examination  and  comparison  of  these  have 

QUESTIONS. — Do  the  various  layers  of  stratified  rocks  extend  uniformly  over  the  whole 
globe?  If  such  were  the  case,  how  could  we  determine  the  relative  age  of  rocks  ?  What 
is  the  reason  that  all  the  stratified  rocks  are  not  everywhere  found  imposed  in  order  upon 
each  other?  How  do  differences  in  mineral  composition  aid  in  determining  the  relative 
age  of  rocks  ?  Illustrate  this  proposition.  Upon  what  evidence  do  geologists  mainly 
rely  for  determining  the  relative  age  of  rocks  ? 


*  "The  mere  place  and  outline  of  the  dry  land  has  frequently  changed.  Most  of  our 
present  dry  lands  have  heen  deep-sea,  and  then  dry  land,  and  then  deep-sea  again,  sev- 
eral times  ;  and  the  same  thing  has  probably  happened  to  those  parts  of  the  earth' s  sur- 
face That  are  now  covered  by  water.  The  solid  crust  of  the  earth  seems  to  have  been 
always  subject  to  a  gentle  fluctuating  movement  of  elevation  and  depression,  affecting 
first  one  area  and  then  another,  while  large  parts  remain  stationary  for  long  periods, 
until  they,  in  their  turn,  are  moved,  and  the  others  left  to  rest.  We  may  look  upon  the 
dry  land  of  any  period,  therefore,  as  merely  so  much  of  the  solid  surface  of  the  earth  as 
happens  to  be  taking  its  turn  to  stand  above  the  level  of  the  sea."— London  Quarterly  Re- 
view, July,  1S59. 

. 


CLASSIFICATION     OF     ROCKS.  169 

established  the  important  fact,  that  different  races  of  animals  and  plants  lived, 
flourished,  and  became  extinct  at  different  epochs  of  the  earth's  history,  and 
have  left  their  forms  impressed  or  imbedded  in  the  rocks  deposited  contem- 
poraneously with  the  period  of  their  existence.  The  fossils,  therefore,  peculiar 
to  each  geological  formation,  or  group  of  rocks,  have  distinct  and  recogniz- 
able characters ;  and  a  geologist  who  has  once  rendered  himself  familiar  with 
these  characters  is  enabled  to  readily  determine,  from  the  presence  of  certain 
forms,  whether  strata,  geographically  remote,  as  in  America  and  Europe,  were 
deposited  at  the  same,  or  at  different  epochs. 

Furthermore,  the  organic  remains  found  in  any  series  of  strata  have  a  dis- 
tinct relation  to  the  circumstances  under  which  the  materials  composing  such 
strata  were  accumulated.  Thus,  it  is  clear  that  the  layers  of  mud,  sand, 
clay,  and  gravel,  depositing  at  the  present  day  in  tropical  seas  and  lakes,  will 
contain  more  or  less  of  the  remains  of  animals  and  plants  peculiar  to  the 
tropics ;  and  deposits  forming  in  temperate  regions  will  contain  in  like  manner 
the  remains  of  animals  and  plants  peculiar  to  temperate  climates ;  and  should 
a  time  arrive,  when  these  layers  are  converted  into  solid  strata,  the  fossilized 
plants  and  animals  contained  in  them  will  become  a  certain  index  to • the 
conditions  of  the  region  at  the  time  of  their  entombment.  And  as  with  de- 
posits now  in  progress,  so  with  strata  constituting  the  solid  crust  of  the 
globe.  Strata  abounding  in  shells,  corals,  and  other  marine  remains,  must 
have  been  deposited  from  the  sea ;  while  those  containing  fresh  water  plants 
and  animals,  mingled  with  the  remains  of  land  animals  and  vegetables,  give 
unmistakable  evidence  of  having  originated  in  lakes  of  fresh  water  or  at  the 
mouths  of  rivers. 

These  and  similar  propositions  are  so  apparent,  that  the  student  can  have 
little  difficulty  in  comprehending  the  principles  upon  which  geologists  have 
proceeded  in  classifying  the  different  rock-formations  of  the  globe. 

169.  As  the  unstratified  or  igneous  rocks  occur  in  no 
regular  order  of  succession,  and  are  not  characterized  by 
the  presence  of  fossils,  their  relative  age  can  only  be  in- 
ferred from,  an  examination  of  the  stratified  rocks  with 
which  they  are  associated.    (See  Fig.  112.) 

Thus,  if  igneous  rocks  are  found  displacing  and  breaking  through  any  set 
of  strata,  they  must  be  more  recent  than  the  strata  disrupted  •  and  if  another 
set  of  strata  overlie  these  igneous  rocks,  then  the  latter  must  have  been  de- 
posited .from  water  at  a  period  subsequent  to  the  igneous  eruptions. 

170.  Progress   of  Geological   Classification,— A  brief  review 

of  the  history  of  the  progress  of  geological  classification  is  almost  indispens- 

QUESTIONS — Illustrate  this  proposition.  What  relation  have  the  organic  remains,  or 
fossils  found  in  strata,  to  the  circumstances  under  which  the  strata  were  formed  ?  Show 
how  this  is.  How  may  the  relative  age  of  the  igneous  rocks  be  inferred  ?  Illustrate  this 
by  example. 

8 


170       FIRST     PRINCIPLES     OF     GEOLOGY. 

able  to  enable  the  learner  to  understand  how  geologists  have  been  led,  step 
by  step,  to  their  present  conclusions,  and  in  what  manner  various  technical 
terms  have  originated  and  been  introduced  into  geological  nomenclature. 

Most  of  the  hypotheses  put  forth  by  the  earlier  philosophers  respecting  the 
geological  structur^  of  the  globe  were  more  curious  than  instructive ;  and  it 
is  only  within  the  last  half  century  that  any  very  correct  notions  upon  the 
subject  have  been  arrived  at. 

In  modern  times,  geological  facts  first  began  to  excite  attention  in  Italy, 
in  the  early  part  of  the  sixteenth  century.  The  strata  of  the  Italian  moun- 
tains are  singularly  rich  in  fossil  shells ;  and  when  these  remarkable  objects 
arrested  the  attention  of  thoughtful  men,  controversies  arose,  whether  they 
were  really  the  remains  of  living  creatures  or  the  productions  of  some  mys- 
terious power  by  which  the  forms  of  such  creatures  were  mimicked ;  and 
again,  if  the  shells  were  really  the  spoils  of  the  sea,  whether  they  had  been 
carried  to  the  hills  by  the  deluge,  of  which  the  Scripture  speaks,  or  whether 
they  indicated  revulsions  of  the  earth  of  a  different  kind.  These  questions 
occupied  the  learned  world  for  nearly  three  centuries. 

One  of  the  first  persons  who  applied  a  sound  and  vigorous  intellect  to 
these  subjects  was  the  celebrated  painter,  Leonardo  da  Tinci,  and  a  philoso- 
pher by  the  name  of  Frascatora,  whose  attention  was  engaged  by  the  multi- 
tude of  curio.us  petrifactions  which  were  brought  to  light,  in  1517,  in  the 
mountains  of  Verona,  in  quarrying  materials  for  repairing  the  city.  They 
exposed  the  absurdity  of  the  theories  which  referred  these  petrifactions  to  a 
certain  plastic  force  in  nature  that  could  fashion  stones  into  organic  forms, 
and  maintained  that  all  fossil  shells  once  belonged  to  living  animals,  and  that 
the  deluge  of  Noah  was  too  transient  an  event  to  explain  the  phenomena.* 

171.  The  truth,  however,  made  but  slow  progress  in  the  face  of  the  estab-' 
lished  prejudices  of  the  times;  and  as  late  as  1617  we  find  distinguished 
Professors  of  Anatomy,  and  learned  men,  in  Italy,  Switzerland,  and  England, 
maintaining  that  the  fossil  ivory  tusks  of  elephants  were  mere  earthy  con- 
cretions, or  that  the  bones  of  elephants,  mastodons,  and  huge  marine  animals, 
found  imbedded  in  the  earth,  were  those  of  giants,  or  even  of  the  fallen  angels. 

172,  In.  1680,  the  celebrated  German  mathematician,  Leibnitz,  first  pro- 
posed the  theory,  that  the  earth  was  originally  in  a  state  of  igneous  fusion, 
and  that  its  solid  crust  was  the  result  of  a  gradual  cooling.     Ho  also  insti- 
tuted a  division  of  rocks  into  stratified  and  unstratified — the  former  term 

QUESTIONS. — What  is  said  of  the  earlier  geological  hypotheses  ?  Where  and  when,  in 
modern  times,  did  geological  facts  first  attract  attention  ?  What  questions  arose  among 
learned  men  respecting  fossil  shells  ?  "Who  were  especially  advocates  of  the  reality  of 
their  former  existence? 


*  "  You  tell  me,"  says  Leonardo  da  Vinci,  in  one  of  his  statements,  "  that  nature  and 
the  influence  of  the  stars  have  formed  these  shelly  forms  in  the  mountains  ;  then  show 
me  a  place  in  the  mountains  where  the  stars  at  the  present  day  make  shells  of  different 
ages  and  of  different  species  in  the  same  place.  And  how  will  j'ou  explain  the  gravel 
which  is  hardened  into  rocks  at  different  heights  in  the  mountains  ?" 


CLASSIFICATION     OF     BOCKS.  171 

embracing  rocks  deposited  from  water,  and  the  latter  those  which  had  con- 
solidated from  a  melted  state. 

173.  In  1756,  Lehmann,  a  German  miner,  proposed  to  divide  rocks  into 
three  classes;    the  first  and  oldest  to  be  called  primitive  (comprising  the 
igneous  and  metamorphic  rocks) ;  the  second  to  be  termed  secondary  (com- 
prehending the  aqueous  or  fossiliferous  strata) ;  while  the  remainder,  or  third 
class,  called  local,  included  the  supposed  effects  of  local  floods,  and  the  de- 
luge of  Noah,  and  corresponded  to  what,  in  modern  classifications,  are  known 
as  alluvium  and  drift.     In  the  primitive  class  (such  as  granite  and  gneiss),  ho 
said,  there  are  no  organic  remains,  nor  any  signs  of  materials  derived  from 
the  ruins  of  preexisting  rocks.     Their  origin,  therefore,  may  have  been  purely 
chemical,  antecedent  to  the  creation  of  human  beings,  and  probably  coeval 
with  the  birth  of  the  world  itself.     The  secondary  formations,  on  the  contrary, 
which  often  contain  sand,  pebbles,  and  organic  remains,  must  have  been 
mechanical  deposits,  produced  after  the  planet  had  become  the  habitation  of 
animals  and  plants.     This  bold  generalization  formed  at  the  time  an  import- 
ant step  in  the  progress  of  geology,  and  sketched  out  correctly  some  of  the 
leading  divisions  into  which  rocks  may  be  separated. — LYELL. 

174.  The  next  important  advance  was  made  by  "Werner,  an   eminent 
German  mineralogist,  Professor  in  a  mining  school  at  Freyburg,  in  Saxony. 
He  asserted  the  existence  of  four  rock  formations,  which  originally  extended 
over  the  whole  globe,  and  followed  each  other  in  an  invariable  order.     The 
first  and  lowest  of  these,  termed  "primary"  or  "primitive,"  included  granite 
— the  basis ;   then  mica-slate  and  clay-slate — rocks  of  a  crystalline  character 
and  wholly  devoid  of  organic  remains.     Resting  upon  these,  Werner  taught 
the  existence  of  a  series  of  strata,  intermediate  in  character  between  the 
older  and  the  newer  formations,  having  to  some  extent  a  crystalline  texture, 
but  yet  exhibiting  occasionally  signs  of  a  mechanical  origin  and  also  a  few 
organic  remains.     For  this  group,  which  apparently  formed  a  connection  be- 
tweed  Lehmann's  primitive  and  secondary  rocks,  he  proposed  the  name  of 
"transition."     The  rocks  belonging  to  it  consisted  principally  of  slates  and 
schists,   an   argillaceous  sandstone,    called    "graywacke,"    and  some   lime- 
stones.    Succeeding  the  transition  were  regular  fossiliferous  strata — sand- 
stones, limestones,  coal,  gypsum,  etc. — which  he  termed  "secondary-"  and  to 
every  deposit  more  modern  than  the  secondary  he  gave  the  name  "  alluvial" 

These  divisions  were  extensively  adopted  by  geologists,  and  have  con- 
tinued to  influence,  more  or  less,  the  systems  of  classification  down  to  the 
present  day.  Tabulated,  they  appear  as  follows  : 

1.  ALLUVIAL — Sand,  gravel,  clay,  etc. 

2.  SECONDARY— Fossiliferous  rocks,  with  a  mechanical  structure. 

3.  TRANSITION— Partially  crystalline,  partially  mechanical,  ami  sometimes  fossili- 

ferous. 

4.  PEIMAEY  OR  PRIMITIVE—  Crystalline,  and  wholly  wanting  in  fossils. 

QUESTIONS. — Did  correct  geological  opinions  soon  receive  the  support  of  scientific  men  ? 
What  theory  was  proposed  by  Leibnitz?  What  divisions  of  rocks  -were  proposed  by 
Lehmann?  Who  next  was  Instrumental  in  advancing  the  science  of  geology?  What 
were  the  views  of  Werner? 


172      FIRST     PRINCIPLES     OF     GEOLOGY. 

"Werner  supposed  that  all  rocks,  the  stratified  as  well  as  the  unstratified, 
were  deposited  from  water ;  and  that  veins  were  filled  by  matter  introduced 
from  above  in  aqueous  solution.  On  account  of  this  reference  of  all  geologi- 
cal deposits  to  water,  his  theory  was  called  "  Neptunian."* 

175.  Nearly  at  the  same  time,  a  Scotch  geologist,  by  the  name  of  Hutton, 
published  a  "Theory  of  the  Earth,"  opposed  in  most  respects  to  the  doctrines 
of  Werner.  He  taught,  that  the  rocks  which  form  our  present  continents 
were  derived  from  the  ruins  of  former  continents,  which  were  abraded  and 
carried  into  the  sea  by  the  agency  of  running  water ;  just  as  the  same  agency 
is  now  spreading  over  the  bottom  of  the  ocean  deposits  of  mud,  sand,  and 
gravel.  Granite  and  trap  rocks,  he  asserted,  were  of  igneous  origin,  and 
have  been  intruded  in  a  melted  state  into  fissures  in  the  earth's  crust.  The 
crystalline  stratified  rocks,  included  in  the  classes  "  primary"  and  "  transi- 
tion," of  Werner,  he  regarded  as  merely  sedimentary  strata,  altered  by  heat 
— a  supposition  which  accords  very  well  with  the  views  at  present  enter- 
tained respecting  the  origin  of  the  metamorphic  rocks.  *} 

These  rival  theories  excited  a  controversy  among  the  scientific  men  of 
Europe,  which  for  years  was  carried  on  with  a  bitterness  and  animosity 
almost  unprecedented  in  the  history  of  such  disputes;  and  all  geologists 
allied  themselves  to  various  schools  or  sects,  under  the  name  of  "  Wemerians" 
or  "  Neptunists ;"  "  Huttonians"  or  "  Plutonists ;"  "  Cosmogonists^  Li  Diluvial- 
ists"  " Fossilists"  etc.,  etc.  The  final  result  was,  that  the  views  of  Werner 
were  almost  universally  abandoned,  and  those  of  Hutton,  in  their  essential 
features,  adopted.f 

QUESTIONS. — To  what  cause  did  "Werner  refer  the  production  of  rocks?  By  what 
name  was  his  theory  designated  ?  Who  especially  opposed  "Werner  ?  What  were  the 
views  advanced  by  Hutton?  What  was  the  result  of  the  promulgation  of  these  different 
geological  views  ? 


*  "  The  theory  of  Werner  assumed  that  the  globe  had  been  first  invested  by  an  universal 
chaotic  ocean,  holding  the  materials  of  all  rocks  in  solution.  From  the  waters  of  this 
ocean,  granite,  gneiss,  and  other  crystalline  formations  were  first  precipitated ;  and 
afterward,  when  the  waters  were  purged  of  these  ingredients,  and  more  nearly  resem- 
bled those  of  our  actual  seas,  the  transition  strata  were  deposited.  These  were  of  a 
mixed  character,  not  purely  chemical,  because  waves  and  currents  had  already  begun  to 
wear  down  solid  land,  and  to  give  rise  to  pebbles,  sand,  and  mud  ;  nor  entirely  without 
fossils,  because  a  few  of  the  first  marine  animals  had  begun  to  exist.  After  this  period 
the  secondary  formations  were  accumulated  in  waters  resembling  those  of  the  present 
ocean,  except  at  intervals,  when,  from  causes  wholly  unexplained,  a  partial  recurrence 
of  the  ' '  chaotic  fluid"  took  place,  during  which,  various  trap-rocks,  some  highly  crystal- 
line, were  formed.  This  arbitrary  hypothesis  rejected  all  intervention  of  igneous  agency 
— volcanoes  being  regarded  as  partial  and  superfluous  accidents,  of  trifling  account  among 
the  great  causes  which  have  modified  the  external  structure  of  the  globe." — LyeWs  Ele- 
ments of  Geology. 

t  At  the  present  day,  the  tendency  among  geologists  is  to  the  belief  that  the  crystalline 
and  compact  condition  of  many  rocks,  which  has  been  heretofore  attributed  to  the  action 
of  dry  heat,  should  be  rather  referred  to  the  agency  of  heated  water,  or  possibly  of  steam 
under  great  pressure.  Thus,  glass,  which  is  a  silicate,  allied  in  composition  to  many  of 
the  hardest  rocks,  can  be  entirely  dissolved  by  the  action  of  water,  heated  under  pressure ; 


CLASSIFICATION     OF     BOOKS.  173 

176.  About  the  beginning  of  the  present  century,  "William  Smith  a  humble 
engineer  in  England,  Saussure  and  Cuvier  of  France,  and  others,  began  to  in- 
vestigate the  structure  of  the  earth's  crust  in  a  more  philosophic  manner. 
Group  after  group  of  strata  were  examined,  and  their  relative  position  and 
fossil  contents  determined  and  compared ;  and  it  was  then  shown,  for  the 
first  time,  that  strata,  very  remote  from  one  another  geographically,  could 
be  identified  as  of  the  same  age  and  position,  by  means  of  the  fossils  con- 
tained in  them. 

177.  As  a  result  of  these  investigations,  the  following  modifications  of 
"Werner's  classification  were  adopted,  and  continued  for  many  years  to  give 
direction  and  consistency  to  the  researches  of  modern  geologists : — 

EECENT.— ^4#  superficial  accumulations,  such  as  sand,  gravel,  marl,  clays, 
peat,  coral-reefs,  etc. ;  which  contain  the  remains  of  existing  ani- 
mals and  plants. 

TERTIARY. — .Local  and  limited  deposits  of  stratified  rocks,  clays,  and  marls, 
lying  below  the  recent  and  above  the  secondary,  and  containing  the 
remains  of  animals  and  plants  not  differing  widely  in  character 
from  those  now  existing. 

SECONDARY. — Strata  of  fossiliferous  rocks,  containing  the  remains  of  animals 
and  plants,  of  species  entirely  different  from  those  now  existing. 
TJiis formation  embraced  all  the  strata  known  as  chalk,  oolite,  lias, 
coal-measures,  and  old  red-sandstone. 

TRANSITION. — Strata  of  slaty  rocks,  argillaceous  sandstones  Jcnown  as  "  gray- 
„  wacke"  limestones,  etc.  ;  containing  few  or  no  fossil  plants,  and  only 

the  remains  ofkno  orders  of  marine  animals,  s7iells,  Crustacea,  corals, 
etc. 

PBIMABY. — All  hard,  compact,  crystalline  rocks,  entirely  destitute  of  all  traces 
of  organic  remains.  In  this  class  were  included  the  clay-slates, 
f/neift*,  mica,  talcose,  and  hornblende  schists,  and  the  various  quartz 
rocks. 

IGNEOUS.— Succeeding  the  primary  rocks,  and  const  farting  the  basis  upon  which 
all  the  other  formations  rest,  was  granite,  and  other  rocks  of  like 
character,  of  assumed  igneous  origin. 

178.  Classifications  of  Modern. Geologists,— As  the  result  of 
a  more  extensive  examination  of  the  stratified  rocks  of  different  countries, 
and  especially  from  the  study  and  comparison  of  their  fossils,  the  above 
noticed  divisions  of  the  earlier  geologists  have  been  for  the  most  part  aban- 
doned, and  more  minute  and  exact  classifications  instituted. 

The  classification  accepted  at  present  by  most  geologists, 
divides  the  stratified  or  aqueous  rocks  of  the  earth's  crust 
into  ten  separate  systems  or  formations,  each  one  of  which 

QUESTIONS.* — What  was  the  condition  of  the  science  of  geology  at  the  commencement 
of  the  present  century  ?  What  classification  of  rocks  was  recognized  by  the  earlier  in- 
vestigators of  this  century?  How  has  a  more  extensive  examination  of  the  strata  of 
different  countries  affected  classification? 


and  in  some  experiments  of  this  nature,  made  by  Danbre'e,  the  silica  of  the  glass  was 
found  to  have  crystallized  in  the  form  of  quartz.  Now,  it  is  not  improbable  that  we 
may  have  had  all  the  forces  of  pressure,  heat,  and  the  dissolving  power  of  water  com- 
bined, in  the  interior  of  the  earth. 


174          FIRST    PRINCIPLES    OF     GEOLOGY. 

includes  a  great  assemblage  of  strata  which,  have  been 
formed  during  the  epoch  of  the  system,  and  have  cer- 
tain fossil  and  mineral  characters  in  common. 

The  strata  included  in  each  system  are,  in  turn,  divided 
into  groups,  each  of  which  is  characterized  by  some  minor 
mineral  or  fossil  peculiarities ;  and  each  group  into  separate 
beds  or  series  of  strata,  all  of  which  may  have  distinctive 
names  expressive  of  some  marked  feature. 

179.  If  for  the  sake  of  illustration  we  compare  the  different  geological  sys- 
tems to  separate  books  (not  all,  however,  of  the  same  size  or  thickness),  con- 
taining a  record  of  the  earth's  past  history,  then  the  groups  into  which  each 
system  is  divided  will  correspond  to  the  separate  parts  of  a  book,  the  beds  or 
series  to  the  chapters,  the  separate  strata  to  the  leaves,  and  the  laminae  com- 
posing the  strata  to  the  lines  of  the  leaves.  The  comparison,  moreover,  will 
seem  still  more  apt,  if  we  bear  in  mind  that  each  geological  system  indicates 
an  entirely  new  era  in  the  history  of  the  earth,  and  each  of  the  subordinate 
groups  and  series  some  partial  revolution  or  change  in  the  previously  estab- 
lished order.  (See  Frontispeice). 

Proceeding  from  the  surface  of  the  earth  downward,  or  from  the  most  re- 
cent system  to  the  most  ancient,  the  modern  classification  of  the  stratified  rocks 
may  be  stated  as  follows : 

(The  learner  will  be  assisted  in  comprehending  the  classification  here  given  ly 
referring  to  Fig.  98,  which  represents  an  ideal  section  of  the  earths  crust.) 

1.  POST-TEBTIARY,  OB  RECENT  SYSTEM,  comprising  all  modern  deposits  of  rivers  and 

lakes,  peat-beds,  coral-reefs,  and  all  the  formations  that  have  been  pro- 
duced during  the  human  or  historic  period.  The  strata  of  this  system  con- 
tain tJie  remains  of  animals  and  plants  belonging  to  species  now  existing. 

2.  TERTIABY  SYSTEM,  embracing  the  great  superficial  deposits  of  water-worn  materials, 

and  bowlders,  known  as  the  "drift;"  and  a  succession  of  regularly  strati- 
fied clays,  sands,  marls,  and  limestones,  which  have  been  arranged  in  four 
groups,  and  named  as  follows  (commencing  with  the  most  recent) :  pleisto- 
cene, pliocene,  miocene,  and  eocene.  These  groups  of  the  tertiary  system 
contain  the  remains  of  animals  and  plants  which  belong  to  species  for  the 
most  part  extinct,  but  not  differing  widely  from  existing  species. 

3.  CHALK,  OB  CRETACEOUS  SYSTEM.     The  fossils  of  this  system  are  chiefly  marine,  and 

belong  to  species  which  are  extinct. 

4.  OOLITIC,  OR  JURASSIC  SYSTEM,  comprising  groups  of  strata  known  as  the  wealden,  the 

oolite,  and  the  lias.  The  strata  of  this  system  abound  in  the  remains  of 
plants  and  animals  (the  most  remarkable  being  tliose  of  huge  reptiles'),  all 
of  which  belong  to  extinct  species  or  genera.* 

QUESTIONS. — Into  how  many  systems  do  modern  geologists  divide  the  stratified  rocks  ? 
What  constitutes  a  system  ?  How  are  systems  divided  ?  To  what  may  these  divisions 
of  the  stratified  rocks  be  compared?  What  does  each  system  and  group  indicate? 
Which  is  the  first  system?  What  are  its  characteristics?  Name  the  second  and  its 
characteristics?  What  is  the  third  system?  What  is  said  of  the  oolitic  system? 

*  For  definition  of  species  and  genera  consult  §  209. 


CLASSIFICATION     OF     ROCKS. 


175 


Periods 


FlG.  98. 
Systems.  Groups. 


Post-       ) 

Tertiary  j 

f  Drift  or 
I  Pleistocene; 

.Tertiary <j  Pleiocene 

j  Miocene 
[  Eocene 


Tliickness  in  ft. 
inN.  America. 


Cretaceous i  Chalk 

I  Greensand 


Alluvium 200—300 

. .  1,200—1,500 

1,000—3,000 


Oolitic  (Wealden 

•     or  -^Oolite 

Jurassic (Lias 

, Triassic . . . 


5,000 


•  •• Permian 861  (in  Kansas) 

f  Coal  measures  "j  7,000 

...  Carboniferous.,  j  Carboniferous  limestones    L     to 
[Conglomerates  J  13,000 


f  Upper 

.Devonian i  Middle          [ 

[  Lower          J 


11,500 


'Upper 1,300 

Middle 4,850 


Lower 5,400 

Taconic  System  of  Emmon's  f 


Ideal  Section  of  the  Earth's  Crust,  showing  the  arrangement  of  the  Stratified  Rocks 
into  Periods,  Systems,  and  Groups;  and  also  (at  the  lose)  the  position  and  relation  of  the 
Igneous  Rocks  to  the  Great  Divisions  of  the  Stratified  Rocks.— (See  also  Frontispeice). 


176          FIBST     PRINCIPLES     OF     GEOLOGY. 

C.  TBIASSIO,  OR  NEW  RED-SANDSTONE  SYSTEM. — This  system  is  made  up  principally  of 
strata  of  red  or  variegated  sandstones  aud  marls,  the  latter  of  which  are  often 
noted  for  containing  great  deposits  of  rock-salt ;  hence,  the  system  is  some- 
times called  "the  saliferous"  (salt  bearing)  system.  It  contains  but  few 
fossils,  which  in  general  resemble  those  found  in  the  oolitic  system 

6.  PERMIAN  SYSTEM,  made  up  principally  of  red-sandstones,  marls,  and  magnesian  lime- 

stones. Its  fossils  are  comparatively  few,  and  are  allied  to  the  systems  below, 
rather  than  to  those  above  it. 

7.  CARBONIFEROUS,  OH  COAL-BEARING  SYSTEM.— This  system  embraces  the  great  coa! 

deposits  of  the  world,  the  "coal  measures,"  as  they  are  termed;  also  great 
beds  of  limestone  and  slates,  which  are  spoken  of  as  "  carboniferous."  This 
system  is  characterized  by  the  presence,  in  the  "coal  measures"  of  the  fossil 
remains  of  a  most  abundant  and  remarkable  tropical  vegetation.  Its  lime- 
stones abound  in  marine  shells,  corals,  etc. 

8.  DEVONIAN,  OR  OLD  RED-SANDSTONE  SYSTEM,  embracing,  in  North  America,  several 

groups  of  red,  brown,  and  gray  sandstones,  shales,  and  slates.  The  fossils  of 
this  system  are  chiefly  those  of  fishes  and  Crustacea  (crabs,  etc.) ;  the  shells 
are  not  numerous,  and  the  plants  are  few  and  imperfect.  2fo  remains  of 
the  higher  animals  are  found  in  this  system. 

9.  SILURIAN  SYSTEM,  divided  into  the  Upper,  Middle,  and  Lower  Silurian  groups.    The 

fossils  of  this  system  are  principally  marine  shells,  corals,  Crustacea,  etc. 
The  remains  of  fishes  occur  only  in  the  strata  of  the  upper  group.  No  land 
plants  nor  remains  of  reptiles,  or  of  any  of  the  higher  orders  of  animals, 
have  ever  been  found  fossil  in  this  division  of  the  stratified  rocks. 

10.  HUBONIAN,  OR  CAMBRIAN  AND  LATTRENTIAN  SYSTEMS.— The  stratified  rocks  under- 

lying the  Silurian  system,  and  which  constitute  the  lowest  and  oldest  mem- 
bers of  the  series,  are  all  more  or  less  metamorphic,  and  are  characteristically 
barren  of  fossils.  They  have  been  divided  by  geologists  into  two  systems  ; 
the  upper  being  variously  named  the  "  Huronian,"  "  Cambrian,"  or  "  Semi- 
Metamorphic ;"  and  the  lower,  the  "  Laurentian,11  "  True  Metamorphic,"  or 
"  Hypozoic"  (below  life)  system.  They  are  also  often  collectively  spoken  of 
asthe"Unfossiliferous,"  "Metamorphic,"  or  "Azoic"  (wanting in  life)  rocks. 

The  basis  upon  which  the  lowest  system  of  the  stratified 
rocks  rest  is  generally  believed  to  be  granite,  or  unstratified 
rocks  of  igneous  origin,  as  is  shown  in  Fig.  98. 

The  beginner  in  geology  will  find  his  progress  greatly 
facilitated  if  he  keeps  steadily  in  view  the  fact,  that  the 
classification  of  the  stratified  rocks  above  given  is  fun- 
damentally chronological;  or,  in  other  words,  that  they 
are  classified  according  to  the  order  of  time  in  which  they 
were  formed. 

180.  From  this  order  of  succession,  moreover,  there  is  no  deviation.  By  this, 
liowever,  it  is  not  to  be  understood  that  all  the  systems  are  to  be  found  at 

QUESTIONS.— What  is  the  fifth  system?  What  are  its  characteristics?  What  is  the 
sixth  system  ?  What  is  the  seventh  ?  What  are  the  characteristics  of  the  carboniferous 
system  ?  What  is  the  next  system  below  this  carboniferous  ?  What  are  the  character- 
istics of  the  Devonian  system  ?  By  what  other  name  is  this  system  sometimes  called  ? 
What  are  the  characteristics  of  the  Silurian  system  ?  What  is  the  lowest  system  ?  What 
is  known  about  it  ?  Upon  what  basis  is  the  lowest  system  supposed  to  rest  ?  What 
is  the  principle  upon  which  the  classification  of  the  stratified  rocks  is  established  ? 


CLASSIFICATION     OF     ROCKS.  177 

any  part  of  the  crust  of  the  earth  lying  one  above  the  other  like  the  coats 
of  an  onion  (and  as  is  the  case  in  the  ideal  section  represented  in  Fig.  98) ; 
but  that,  wherever  the  rocks  of  two  or  more  systems  come  together,  they  are 
never  found  out  of  place ;  that  is,  the  rocks  of  the  Carboniferous  system  are 
never*  found  beneath  those  of  the  Silurian ;  or  those  of  the  Oolite  beneath 
the  Carboniferous ;  or,  in  short,  any  rocks  of  a  higher  system  beneath  those 
of  a  lower. 

Furthermore,  as  any. particular  area  of  the  earth  may  have  been  an  area 
of  destruction  (erosion  and  degradation)  during  one  period,  and  an  area  of 
production,  or  even  of  neutrality  during  another,  strata  of  one  system  may 
rest  directly  upon  those  belonging  to  a  much  older  system,  without  the  pres- 
ence of  the  naturally  intervening  series.  Thus,  for  example,  the  rocks  of 
the  Devonian  system  and  those  of  the  Silurian  might,  in  some  districts,  be 
wholly  wanting ;  and  in  this  case  the  strata  of  the  Carboniferous  system  would 
rest  directly  upon  those  of  the  Huronian ;  or  the  Oolite,  Triassic,  and  Permian 
rocks  being  absent,  the  Cretaceous  would  rest  directly  upon  the  Carbonifer- 
ous. In  every  such  case,  the  principle  that  the  higher  system  invariably 
overlies  the  lower,  would  be  maintained ;  while  a  reversal  of  the  order  of 
succession,  from  the  nature  of  the  case,  would  be  impossible. 

181.  The  learner  must  here  be  cautioned  against  supposing  that  the  rocks 
which  make  up  the  different  systems  are  so  different  from  each  other  in 
appearance  as  to  admit  of  easy  recognition  by  mere  inspection.      On  the 
contrary,  the  varieties  of  stratified  rocks  are  comparatively  few,  and  each 
system  contains  limestones,  sandstones,  and  argillaceous  (clay)  rocks,  which 
do  not  differ  materially  in  appearance  or  composition  from  similar  rocks  in 
other  systems. 

This  circumstance,  however,  occasions  but  little  embarrassment  to  the 
geologist,  for  the  reason  that  the  fossils  found  in  each  of  the  different  systems 
of  rocks  are  peculiar  and  different  from  those  of  any  other  system ;  so  that, 
although  sandstones  from  the  Oolite  may  exactly  resemble  sandstones  from 
the  Carboniferous  system,  or  limestones  from  the  Devonian  system  those  from 
the  Silurian,  yet  an  experienced  geologist,  by  the  difference  of  their  contained 
fossils,  is  at  once  enabled  to  designate  their  true  character  and  the  relative 
ago  of  their  formation. 

182.  Division  of  Geological  Time  into  Periods  or  Ages, 
— Each  system  of  stratified  rocks,   as   has  been  before 
stated,  contains  fossils  peculiar  to  itself,  and  these  do  not 
ever  recur  in  strata  belonging  to  contiguous  systems  either 
above  or  below  it  in  the  order  of  succession.     At  the  same 


QUESTIONS.— What  is  understood  by  the  invariable  order  of  succession  of  the  different 
systems?  Explain  how  it  happens  that  some  systems  of  rocks  are  wanting  in  certain 
localities?  Are  the  rocks  belonging  to  each  system  peculiar  in  their  appearance ?  If, 
then,  they  are  alike,  how  can  a  geologist  refer  them  to  different  systems? 


178       FIRST     PRINCIPLES     OF     GEOLOGY. 

time,  there  is  a  connection  between  the  different  systems 
more  strong  in  proportion  to  their  proximity  to  each  other. 
The  fossils  of  the  Cretaceous  system,  while  they  differ  from 
those  of  all  other  systems,  are  nevertheless  much  more 
nearly  related  to  those  of  the  Oolite  system,  which  immedi- 
ately precedes,  than  to  those  of  the  Carboniferous  system, 
which  is  much  more  ancient ;  and  in  the  same  manner 
the  fossils  of  the  Carboniferous  approach  more  nearly  those 
of  the  Silurian  system  than  those  of  the  Tertiary. 

These  relations  have  suggested  to  geologists  and  natur- 
alists a  classification  of  the  different  systems  of  rocks 
according  to  the  general  type  or  character  of  the  living 
beings  which  predominated  during  certain  periods  or  ages 
of  the  earth's  history;  just  as  in  the  history  of  man  several 
grand  periods  or  ages  have  been  established,  which  are 
marked  by  peculiarities  in  his  social  and  intellectual  condi- 
'tion,  and  are  illustrated  by  contemporaneous  monuments. 

The  names  applied  to  these  several  periods  are  derived  from  tho  Greek, 
and,  commencing  with  the  most  recent,  are  as  follows: 

1.  Cainozoic  (naivo?,  recent,  and  &i],  life),  or  period  of  recent  life.     This 
period  includes  the  Post- Tertiary,  or  recent  system  of  rocks,  and  the  Tertiary 
system. 

2.  M  e  s  o z  o  i  c  (peaoc.,  middle),  or  the  period  of  middle  life.     This  period 
includes  the  Cretaceous,  Oolitic,  and  Triassic  systems. 

3.  Paleozoic  (na^aiac.,  ancient),  or  period  of  ancient  life.     This  period 
includes  the  Permian,  Carboniferous,  Devonian,  and  Silurian  systems. 

4.  Azoic  (a,  privative,  and  frv,  life),  or  tho  period  deficient  in  the  evi- 
dences of  life.     This  period  includes  the  Laurentian  rocks,  or  all  the  unfossili- 
ferous  and  metamorphic  rocks  which  lie  below  the  base  of  rocks  included  in  the 
Paleozoic  period,  and  which  have  thus  far  yielded  little  or  no  evidence  of  the 
existence  of  life  at  the  time  of  their  deposition* 

QUESTIONS. — What  differences  and  points  of  resemblance  exist  between  different  sys- 
tems? What  classification  of  the  geological  systems  has  been  established  ?  What  anal- 
ogy exists  between  the  periods  or  ages  in  geology  and  the  periods  instituted  in  the  history 
of  man  ?  What  is  the  first  or  most  recent  period  ?  What  systems  does  it  include  ?  What 
is  the  second  period  ?  What  systems  does  it  include  ?  What  is  the  third  period  ?  What 
systems  are  included  in  it  ?  What  is  the  fourth  period  ?  What  arc  the  systems  included 
in  it? 

*  The  relation  of  the  geological  periods  to  the  several  systems  is  clearly  shown  in  Fig. 
98,  in  the  pependicular  section,  on  the  left.  Their  relation  to  each  other,  and  to  the 
igneous  or  unstratified  rocks  is  also  shown  at  the  base  of  the  same  figure. 


CLASSIFICATION     OF     KOCKS.  179 

183.  By  this  arrangement  we  understand,  therefore,  that  during  certain 
epochs  there  was  a  certain  typical  or  general  resemblance  among  the  beings 
then  populating  the  globe ;  that  down  to  the  Cretaceous  system  (i.  e.,  the  recent 
period)  the  fossil  species  closely  resemble  those  now  existing;  from  the  Cre- 
taceous to  the  Permian  (i.  e.,  the  middle  period)  the  departure  from  recent 
forms  was  greater ;  from  the  Permian  to  the  Silurian    (i.  e.,  the  ancient  life 
period)  the  species  were  altogether  distinct  from  the  recent,  and  different,  in 
a  majority  of  instances,  from  those  of  the  middle  period  ;  and  that  from  the 
Silurian  downward   (i.  e.,  the  period  deficient  in  life)  traces  of  organic  life  are 
very  obscure,  or  altogether  wanting. 

184.  In  recognizing  these  classifications  "the  student  should  remember — 
and  he  can  not  be  too  early  cautioned  to  bear  ever  in  mind — that  throughout 
the  whole  of  creation  there  is  only  ONE  SYSTEM,  and  that,  in  time  past  as  in 
time  present,  every  aspect  of  nature  gives  evidence  of  only  ONE  all-pervading, 
all-directing  MIND.     The  matter  of  the  universe  may  undergo  change  of  place, 
appearance,  and  arrangement ;  still  it  is  the  same  matter,  and  is  subject  to 
the  same  laws  that  have  operated  through  all  time.     The  plants  and  animals 
may  assume  different  specific  aspects  at  different  epochs  and  under  different 
conditions,  still  they  are  constructed  on  the  same  plan  and  principle,  and  the 
laws  which  influence  their  being  now,  are  identical  with  those  which  have 
governed  life  since  the  dawn  of  creation.     "Without  this  uniformity  of  law 
the  study  of  nature  would  be  impossible.     There  is  only  ONE  GREAT  SYSTEM 
in  creation,  and  the  periods  and  systems  of  the  geologist  must  be  regarded  as 
mere  provisional  expedients  toward  the  elucidation  and  comprehension  of  that 
system." 

185.  Geological  Nomenclature, — To  beginners,  the  nomenclature 
employed  by  geologists  is  often  exceedingly  difficult  to  understand,   and 
seems  to  render  the  whole  subject  needlessly  obscure.     The  reason  of  this  is 
undoubtedly  due  in  part  to  the  double  signification  of  many  of  the  terms 
used  by  geologists  to  designate  stratified  rock-groups,   or  systems.      The 
original  name  given  by  the  early  observers  to  a  system  or  group  of  strata, 
was  often  descriptive  of  the  kind  of  stone  of  which  it  was  principally  com- 
posed, or  the  most  important  mineral  substance  it  contained.     Thus,  the  Cre- 
taceous system  was  so  named,  because  in  the  district  in  which  it  was  first 
studied  a  large  part  of  it  consisted  of  chalk  (Lat.,  creta) ;  the  Oolitic  system, 
in  like  manner,  contained,  in  the  typical  district,  many  beds  of  oolitic  lime- 
stone (see  §  15);  and  the  Carboniferous,  many  beds  of  coal.     Other  names 
had  a  geographical  signification,  such  as  Devonian — 'the  formations  to  be  seen 
in  Devonshire,  England ;  Silurian — those  in  the  district  of  "Wales,  the  ancient 
Siluria.     As  soon,  however,  as  extended  observation  showed  that  all  the 
aqueous  rocks  occurred  in  a  certain  order,  and  formed  a  series  or  succession 

QUESTIONS. — What  is  to  be  understood  by  this  arrangement  of  geological  time  into  four 
periods  ?  Is  there  in  any  of  these  classifications  any  evidence  of  a  diversity  of  plan  on 
the  part  of  the  Creator  ?  Explain  how  it  is  that  many  geological  terms  have  acquired  A 
double  signification. 


180        FIRST     PRINCIPLES     OF     GEOLOGY. 

of  beds  regularly  and  invariably  superimposed  upon  each  other,  these  terms 
lost  their  original  import  and  acquired  a  purely  chronological  meaning.  Thus, 
for  example,  when  we  trace  the  Devonian  or  Silurian  rocks  beyond  the  bor- 
ders of  the  district  where  they  were  first  observed,  it  is  clear  that  the  strictly 
geographic  term  becomes  no  longer  applicable.  It  is,  moreover,  somewhat  of  a 
contradiction  to  speak  of  Silurian  or  Devonian  rocks  as  existing  in  the  State 
of  New  York,  or  in  India.  But  what  is  meant  is,  that  the  Silurian  or  Dev- 
onian rocks  of  America  or  Asia  are  a  continuation  of  those  of  Wales  or  Devon- 
shire; or,  in  other  words,  that  they  were  deposited  together  with  them,  at 
the  same  epoch,  in  similar  seas,  and  contain  similar  fossils. 

In  like  manner,  when  we  come  to  trace  the  Cretaceous,  Oolite,  or  Carboni- 
ferous systems  from  one  area  to  another,  it  often  happens  that  the  nature 
of  the  rock  gradually  changes.  Each  system  consists  of  a  vast  number  of 
separate  beds  of  rock,  every  one  of  which  varies  almost  indefinitely  in  ex- 
tent. The  beds  of  coal,  which  gave  their  name  to  the  Carboniferous  rocks, 
because  of  their  economical  importance,  are  very  few  compared  with  the 
whole  bulk  of  the  rocks  in  the  Carboniferous  system,  and  sometimes  get 
thinner  and  fewer  till  they  disappear  altogether;  while  the  other  portion 
goes  on  and  spreads,  perhaps  over  large  areas,  in  which  we  may  have  the 
apparent  contradiction  of  Carboniferous  rocks  almost  or  entirely  destitute  of 
any  carbonaceous  matter.  In  like  manner,  the  Oolitic  system  in  many  parts 
of  the  world  contains  no  oolites,  and  the  Cretaceous  system  no  chalk.  In 
South  America  the  Cretaceous  system  consists  of  clay-slates,  not  differing  in 
any  essential  character  as  a  kind  of  rock  from  the  slates  found  in  the  Silurian 
system ;  but  the  contained  fossils  are  similar  to  those  of  the  chalk  formations 
of  Europe.  Therefore,  in  speaking  of  Cretaceous  rocks,  we  mean  merely  rocks 
that  were  consolidated  at  an  epoch  which  was  especially  characterized  by  tho 
formation  of  the  chalk  of  Europe,  and  so  of  other  similar  terms. 


CHAPTER    X. 

PALEONTOLOGY.— GENERAL   CHARACTERISTICS   OF  FOSSILS. 

186.  Paleontology.— That  department  of  geological 
science  which  treats  of  the  forms  and  conditions  of  life 
which  prevailed  during  the  former  epochs  of  the  earth's 
history,  is  termed  Paleontology. 

QUESTIONS. — What  do  -we  mean  when  we  say  that  Devonian  or  Silurian  rocks  occur  in 
America  or  Asia  ?  Do  the  Cretaceous  or  Carboniferous  rocks  necessarily  abound  in 
chalk  or  coal  ?  What  is  that  department  of  geology  which  treats  of  the  former  life  of  the 
globe  termed  ?  What  is  the  derivation  of  the  term  ?  (See  §  1.) 


CH  AB  ACT  EKISTIC  S     OF     FOSSILS.          181 

The  only  data  which  can  afford  us  evidence  on  this  sub- 
ject are  the  fossils  found  in  the  rocks  of  the  various  geo- 
logical periods  or  systems.  (See  §  22.) 

187.  Fossils,  whether  vegetable  or  animal,  are  generally 
converted  into  the  same  substance  as  the  rock  in  which 
they  are  imbedded ;  that  is,  if  occurring  in  limestone,  they 
will  be  more  or  less  calcareous  ^  if  in  coal,  carbonaceous ; 
and  if  in  sandstone,  more  or  less  arenaceous  (sandy). 
Sometimes,  however,  the  fossils  are  converted  into  mineral 
matter,  altogether  different  from  the  containing  rock. 

In  numerous  instances  the  form  and  bulk  of  the  organ- 
ism is  entire  and  perfect,  and  may  even  retain  something 
of  the  color  which  it  had  when  alive. 

Thus,  the  shells  found  in  some  of  the  tertiary  rocks  of  the  southern  States 
exhibit  tints  and  markings  of  color  almost  as  bright  as  those  of  the  shells  now 
living  on  the  adjoining  Atlantic  coast.  Insects  occur,  perfectly  preserved, 
sealed  up  in  amber — a  fossil  resin ;  and  in  Siberia,  the  entire  carcass  of  a  fossil 
rhinoceros,  with  the  skin  and  flesh  preserved,  has  been  taken  from  a  stratum 
of  frozen  sand. 

In  other  instances,  the  substance  of  the  animal  or  plant 
has  been  altogether  removed,  so  that  merely  an  impression 
of  its  external  surface,  or  a  mold  6f  its  form,  is  left  in  the 
rock  that  inclosed  it. 

After  this  mold  has  been  formed,  it  may  become  so 
filled  with  mineral  matter,  infiltrated  through  the  pores 
of  the  rock,  as  to  present  a  perfect  cast  or  model  of  the 
fossil  that  was  originally  imbedded. 

In  other  instances,  the  fossil  consists  of  merely  the  impression  of  a  part  of 
the  body  of  an  animal,  as  a  foot-print,  for  example.* 

Different  forms  of  fossils  are  common  in  every  group  or  system  of  the 
fossiliferoua  rocks,  and  by  a  little  practice  the  eye  of  the  student  will  readily 

QUESTIONS.— Where  do  we  find  evidence  on  this  subject  ?  What  are  fossils  ?  (See  § 
22.)  In  what  state  are  the  remains  of  animals  and  plants  generally  preserved  as  fossils  ? 
To  what  extent  are  plants  and  animals  sometimes  preserved  as  fossils  ?  When  is  a  mold 
or  cast  of  the  organism  only  preserved  ? 


*  The  teacher  (or  the  student  for  himself)  will  derive  great  advantage  by  procuring, 
and  subjecting  to  examination,  specimens  of  fossils — plants  and  animals — in  their  various 
conditions  of  preservation.  Such  specimens  can  readily  be  obtained  with  little  trouble, 
or  may  be  purchased  at  a  Blight  expense.  (See  Appendix.) 


182    FIEST    PRINCIPLES    OF    GEOLOGY. 

detect  the  slightest  trace  of  organized  structure  in  any  mass  of  mineral  matter ; 
and  where  the  naked  eye  may  fail,  a  common  pocket  magnifier  will  often  en- 
able an  observer  to  detect  the  presence  of  an  organism. 

188.  Petrifaction,  generally  speaking,  consists  in  the  in- 
filtration of  stony  matter  into  the  pores  of  vegetable  or 
animal  substances. 

"In  some  specimens  the  organic  body  has  entirely  disappeared,  and  the 
stony  matter  has  been  so  gradually  substituted,  particle  for  particle,  that  the. 
petrifaction  presents  a  perfect  resemblance  in  its  minutest  parts  to  the  original 
structure.  It  is  as  if  a  house  were  gradually  rebuilt,  brick  by  brick  or  stone 
by  stone— a  brick  or  a  stone  of  a  different  kind  having  been  substituted  for 
each  of  the  former  ones,  without  either  the  shape  or  size  of  the  house,  or  the 
form  or  arrangement  of  one  of  its  rooms,  passages,  or  closets,  or  even  the 
number  and  shape  of  the  bricks  and  stones,  having  been  altered.  All  the 
hollow  spaces  are,  however,  generally  filled  up  either  by  the  earthy  matters 
in  which  the  fossil  is  inclosed,  or  by  mineral  substances  which  have  perco- 
lated through  their  walls." 

Lime  (in  the  form  of  a  carbonate)  and  silica,  held  in 
solution  in  water,  are  the  most  abundant  petrifying  sub- 
stances. 

The  same  result  is  also  sometimes  produced  through  the  agency  of  metallic 
salts  contained  in  water,  especially  by  the  sulphuret  and  oxyd  of  iron ;  and 
we  find,  not  unfrequently  imbedded  in  strata,  bones,  shells,  and  fishes,  which 
have  been  almost  entirely  converted  into  iron-pyrites  (crystals  of  sulphuret 
of  iron),  with  a  nearly  perfect  retention  of  form. 

In  other  instances,  the  organism  is  converted  into  coal  or  bitumen.  Hugh 
Miller,  in  describing  the  fossil  fishes  found  in  the  Old  Red-sandstone  (Devonian), 
says,  that  their  muscles,  blood,  etc.,  have  been  converted  into  a  kind  of  pitch 
or  bitumen,  which  in  some  places  pervades  the  rock  to  such  an  extent  as  to 
cause  it  to  be  mistaken  for  coal;  and  this  animal  pitch,  by  its  antiseptic 
properties,  has  preserved,  in  all  their  elasticity,  the  bones,  fins,  and  scales 
enveloped  in  it,  better  than  the  oils  and  gums  applied  by  the  old  Egyptians 
to  their  mummies. 

Incrustations  not  Petrifactions, — Organic  substances,  i.  e.,  moss, 
twigs,  leaves,  etc.,  which  have  been  exposed  to  the  action  of  mineral  waters, 
and  have  thereby  become  incrusted  with  calcareous  or  silicious  matter  (see 
§  64)  are  very  often  erroneously  termed  petrifactions  ;  since  in  such  cases 
the  object  is  merely  coated  with  the  stony  matter,  and  not  fully  permeated 
by  it.  • 

QUESTIONS. — What  is  petrifaction  ?  To -what  extent  is  petrifaction  sometimes  carried? 
What  may  the  process  be  compared  to  ?  What  are  the  most  abundant  petrifying  sub- 
stances ?  What  substances  occasionally  act  as  petrifiers  ?  What  are  illustrations  of  this  ? 
What  is  the  difference  between  incrustations  and  petrifactions  ? 


CLASSIFICATION     OF     FOSSILS.  183 

Theory  of  Petrifaction  • — Petrifaction  is,  undoubtedly,  a  chemical 
process,  but  the  exact  manner  in  which  it  takes  place  has  never  been  satis- 
factorily explained,  neither  has  it  been  successfully  imitated.*  Some  authori- 
ties have  supposed  that  petrifaction  is  effected  suddenly  by  the  combination 
of  gaseous  fluids  with  the  constituent  principles  of  the  organic  structure.  In 
some  instances  it  would  appear  certain,  that  the  conversion  of  the  animal  or 
vegetable  substance  into  silica  or  lime  must  have  been  almost  instantaneous, 
for  the  most  delicate  parts — those  which  would  undergo  decomposition  with 
the  greatest  rapidity — are  often  preserved ;  such,  for  example,  as  the  capsule 
of  the  eye,  the  membranes  of  the  stomach,  the  soft  bodies  of  shell-fish,  and, 
in  plants,  the  most  delicate  tissues.  In  specimens  of  petrified  wood,  it  may 
be  often  observed  that  the  petrifaction  did  not  commence  until,  the  wood  had 
begun  to  decay,  since  the  decayed  part,  and  even  the  mould  upon  it,  are 
preserved  as  perfectly  as  the  solid  wood.  The  apparently  delicate  vegetable 
fibres,  sometimes  seen  in  polished  sections  of  agate  or  chalcedony,  especially 
in  the  so-called  umoss  agates,"  are  generally  produced  by  oxyd  of  iron  or 
manganese ;  but  in  some  instances  they  have  been  proved  to  be  really  the 
remains  of  marine  plants,  which  have  become  involved  in  the  silica  when  it 
was  in  a  fluid  state. 

M.  Gceppert,  a  German  geologist,  placed  leaves  of  fern  in  clay,  dried  them 
in  the  shade,  and  exposing  the  clay  to  a  red-heat,  obtained,  in  this  way, 
striking  resemblances  to  fossil  plants.  According  to  the  degree  of  heat,  the 
plant  was  found  to  be  either  brown,  shining  black,  or  entirely  lost — the  im- 
pression only  remaining ;  but  in  the  latter  case  the  surrounding  clay  was 
stained  black  by  the  diffusion  of  Ihe  particles  of  carbon  derived  from  the 
leaves,  and  resembled  the  shales  and  slates  that  are  associated  with  coal. 

189.  Classification  of  the  Animal  and  Vegetable  King- 
dom,—In  order  to  rightly  understand  the  facts  which  the 
study  of  fossils  have  brought  to  light  concerning  the  past 
history  of  the  earth,  it  is  necessary  to  have  some  knowl- 
edge of  existing  animals  and  plants. 

Vegetable  life  subsists  upon  inorganic  food — matters  that  may  be  found 
in  the  earth,  the  water,  or  the  air,  independently  of  animal  life ;  while  ani- 
mal life  subsists  entirely  upon  organic  food,  either  of  vegetable  or  animal 

QUESTIONS. — Is  it  known  how  petrifaction  is  occasioned  ?  What  have  been  some  of  the 
suppositions  on  the  subject  ?  .  In  what  manner  has  the  production  of  fossil  plants  been 
imitated  ?  In  order  to  fully  understand  the  facts  of  palaeontology,  what  is  necessary  ? 


*  Some  years  since  a  Florentine  physician  claimed  to  have  discovered  a  method  of 
artificially  petrifying  animal  substances,  and  at  the  same  time  perfectly  preserving  their 
color  and  internal  structure.  The  specimens  exhibited  by  him  appeared  to  confirm  his 
assertions,  and  there  is  now  in  one  of  the  Italian  museums  a  table,  in  which  different 
portions  of  the  human  body,  petrified,  cut,  and  polished,  are,  inserted  as  Mosaics.  The 
secret,  however,  was  never  revealed  by  the  discoverer,  and  died  with  him. 


184       FIRST     PRINCIPLES     OF     GEOLOGY. 

origin.  It  would,  therefore,  follow,  that  no  plant-eating  animal  could  con- 
tinue to  live  unless  vegetable  life  already  existed  in  sufficient  abundance  to 
serve  as  its  food ;  and  no  flesh-eating  animal  could  exist  until  there  was  an 
abundance  of  plant-eating  animals.  The  order  of  existence,  therefore,  of 
organic  beings  may  be  assumed  to  be — 1st,  plants;  2d,  plant-eating  animals; 
3d,  animal-eating  animals. 


FIG.  99. 


FIG.  100. 


THE  VEGETABLE  KINGDOM. 

190.  Vegetables  have  been  arranged  in  two  grand  divi- 
sions : 

1st,  PHANEROGAMIA;  OR  FLOWERING  PLANTS. 
2d;  CRYPTOGAMIA,  OR  FLOWERLESS  PLANTS. 

191.  Phanerogam! a, — The  first  division  (Phanerogamia) 
embraces  all  the  higher  forms  of  vegetation  ;  and  all  the 
plants  included  in  it  bear  true  flowers  and  produce  seeds. 
It  naturally  subdivides  into  two  classes — EXOGENS  (out- 
side growers),  and  ENDOGENS  (inside  growers). 

192.  The  Exogens  comprise  all  those  plants  which  increase  by  additions 
of  woody-fiber  to  the  outside — a  new  layer  being  added  each  year  just  beneath 
the  bark,  to  the  previous  growth.     Hence,  the  ago  of  an  exogenous  plant  is 
indicated  by  the  number  of  con- 
centric ringa  exhibited  by  a  cross 

section  of  its  stem  or  trunk.  The 
leaves  of  exogenous  plants  have 
also  net-like  veins.  All  our  forest 
trees  and  shrubs  belong  to  this 
class.  A  slice  across  an  exogen- 
ous stem  shows  a  separate  cellu- 
lar part,  as  bark,  on  the  circum- 
ference; then  a  ring  of  wood ;  and  in  the  center  a  pith,  as  is  seen  in  Tig.  99, 
which  represents  a  piece  of  flax  stem  magnified;  and  also  in  Fig.  100,  which 
is  a  stem  of  maple  of  a  year  old,  cut  crosswise  and  lengthwise. 

193.  The  Endogons  embrace  all  flowering  plants,  whose  stems  are  not 
composed  of  concentric  layers,  but  whose  woody  substance  is  mixed  with 
pith  and  distributed  throughout  every  part  of  the  stem  in  the  form  of  threads 
or  bundles.     They  have  almost  always  parallel- veined  leaves,  which  sheath 

QUESTIONS. — What  may  be  supposed  to  be  the  order  of  existence  of  organic  beings? 
How  have  plants  been  classified  ?  What  are  embraced  in  the  first  great  division  ?  What 
are  the  characteristics  of  the  exogenous  plants  ?  What  plants  belong  to  the  class  Endo- 
gens? 


CLASSIFICATION     OF     ANIMALS. 


185 


the  stem,  and  decay  without  falling  off.    Their  bark  also  can  never  be  peeled 

off  clean  from  the  wood.     This  class  of  plants  comprises  the  lilies,  palms,  canes 

FIG  101  (sugar»  and  Indian  corn),  rushes,  and  grasses.     Fig.  101 

shows  an  endogenous  stem  of  a  corn  stalk,  cut  both 

crosswise  and  lengthwise. 

194.  The  Cryptogamia,  or  flowerless 
plants,  produce  no  real  flowers,  and  no 
true  seeds  ;  but  only  something  of  a  sim- 
pler sort,  answering  to  flowers,  and  giving 
rise  to  minute  and  very  simple  bodies, 
which  serve  the  purpose  of  seeds,  and  are 
called  spores.  This  division  comprises 
all  the  lowest  forms  of  vegetation,  and  is 

subdivided  into  three  classes,  ACROGENS,  ANOPHYTES  and 

THALLOPHYTES. 

195.  The  Acrogens  comprise  those  plants  whoso  growth  is  wholly  or 
mainly  at  the  summit. 

This  class  includes  tho  Fern  family  (the  brakes) ;  the  Equicetaceos,  or  horse- 
tail and  cat-tail  family ;  and  the  Club-mosses* 

The  Anophytes  comprise  the  true  mosses. 

The  Thallophytes  comprise  the  algce,  or  sea- weeds;  the  Lichens  (which  in- 
crust  stones  and  decaying  trees);  the  Confervce  (green  scum,  like  aquatic 
growths) ;  and  the  Fungi  (mushrooms,  puff-balls,  toads-tools,  etc.). 

Such  are  the  fundamental  groupings  of  existing  plants,  and  so  constant 
are  the  characters  which  distinguish  these  great  natural  groups,  that  an  ex- 
perienced botanist  or  palaeontologist  by  inspecting  simply  the  fragments  of  a 
leaf,  or  a  portion  of  the  structure  of  a  stem,  can  at  once  decide  on  the  naturo 
of  the  plant  to  which  it  belonged. 


THE  ANIMAL   KINGDOM. 

196.  Animals,  according  to  Cuvier,  may  be  arranged 
in  four  great  divisions  or  sub-kingdoms — VERTEBRATA, 
MOLLUSCA,  ABTICULATA,  and  KADIATA. 

QUESTIONS.— What  are  some  of  the  plants  of  this  class  ?  What  plants  are  embraced  in 
the  second  great  division  ?  Into  what  three  classes  are  the  Cryptogamia  divided  ?  What 
are  the  Acrogens  ?  What  the  Anophytes  ?  What  the  Thallophytes  ?  Are  the  characters 
which  mark  the  great  divisions  of  plants  constant?  How  is  the  animal  kingdom  divided? 

•  The  trailing  evergreens,  used  for  Christmas  decorations,  are  familiar  examples  of  the 
club-mosses. 


186       FIRST      PRINCIPLES      OF      GEOLOGY. 

All  the  animals  in  any  one  of  these  divisions  arc  built  upon  the  same  plan, 
or,  in  other  words,  after  the  same  type. 

197.  I.  Vertebral  a, — All  the  animals  belonging  to  tins 
division  have  a  back-bone  (vertebree),  and  an  internal  skele- 
ton. (See  Fig.  102,  which  represents  a  section  of  the 
body  and  skeleton  of  a  quadruped.)  Thus,  men,  elephants, 
whales,  birds,  reptiles,  and  fishes,  notwithstanding  their 
manifold  differences,  have  these  characters  in  common ; 
they  are  all  back-boned  ;  they  all  have  an  internal  skele- 
ton ;  they  are  all  formed  upon  the  same  plan.'-5 

FIG.  102. 


The  Yertebrata  are  divided  into  four  classes  :  1,  Mam- 
mals (animals  that  suckle  their  young)  ;  2,  Birds  ;  3, 
Keptiles  ;  4,  Fishes. 


QUESTIONS. — What  characterizes  the  animals  of  these  divisions  ?  What  animals  belong 
to  the  class  vertebrata  ?  Why  are  the  vertehrata  so  called  ?  Into  what  classes  are  the 
vertebrata  divided  ? 


*  The  fact  that  all  the  animals  included  in  this  division  or  sub-kingdom  (Vertebrata) 
are  formed  upon  one  plan,  -will  be  made  more  clear  if  we  institute  a  comparison  between 
the  skeletons  of  different  vertebrate  animals.  "  Thus,  every  bone  in  the  body  of  a  lizard 
has  a  corresponding  bone  in  the  body  of  a  man,  or  of  a  mouse ;  and  every  bone  preserves 
the  same  connection  with  other  bones,  no  matter  how  unlike  may  be  the  various  limbs 
in  which  we  detect  its  presence.  Thus,  widely  as  the  arm  of  a  man  differs  from  the  fin 
of  a  whale,  or  the  wing  of  a  bird,  or  the  wing  of  a  bat,  or  the  leg  of  a  horse,  the  same 
number  of  bones  and  the  same  connections  of  the  bones  are  found  in  each.  A  fin  is  one 
modified  form  of  a  typical  limb;  an  arm  is  another;  a  wing  another.  That  which  is 
true  of  the  limbs  is  also  true  of  all  the  organs ;  and  it  is  on  this  ground  that  we  speak 
of  the  vertebrate  type.  From  fish  to  man,  one  common  plan  of  structure  prevails." 


CLASSIFICATION     OF     ANIMALS.  187 

All  mammals  resemble  each  other  more  than  they  resemble  birds ;  all  rep- 
tiles resemble  each  other  ]npre  .than  they  resemble  fishes  (notwithstanding  a 
superficial  resemblance  between  serpents  and  eels). 

Each  class  is  susceptible  of  still  more  minute  division  into  orders.  Thus, 
of  the  mammalia,  those  which  live  upon  flesh  are  grouped  in  one  order, 
carnivora ;  those  which  live  upon  plants  constitute  the  order  herbivora ;  and 
those  which  resemble  whales,  the  order  cetacea.  In  like  manner,  birds  are 
grallatores  (waders) ;  natatores  (swimmers),  etc. ;  and  reptiles  are  tatrachian 
(frog-like) ;  saurian  (lizard-like) ;  ophidian  (serpent-like),  etc. 

Fishes  are  divided,  as  they  exist  in  the  present  creation, 
into  two  orders — "  osseous"  and  "cartilaginous" — accord- 
ing as  they  are  furnished  with  a  skeleton  of  bone;  or  of  car- 
tilage (gristle).'-5 

In  each  order  there  are  generally  families ;  and  the  families  separate  into 
genera,  which  differ  from  each  other  only  in  fewer  and  less  important  charac- 
ters. The  genera,  in  turn,  include  groups,  which  have  still  fewer  differences, 
and  are  called  species ;  and  these  again  are  divided  into  other  groups,  which 
have  only  minute  and  unimportant  differences  of  color,  size,  and  the  like,  and 
are  called  sub-species  or  varieties,  f 

198.  II.  Mollusca, — Animals  of  this  division  have  no 
internal  skeleton,  and  are  -all  soft-bodied  ;  (hence,  their 
name  from  the  Latin  mollis,  soft).  Their  nervous  sys- 
tem is  dispersed  through  their  body  in  irregular  masses  ; 
their  muscles  are  attached  to  the  skin,  which  in  many 
species  is  covered  by  a  shell  (as  oysters,  snails,  cuttle- 
fish, etc.).  This  division  embraces  three  classes. 

QUESTIONS.— What  is  said  of  the  division  of  classes  into  orders  ?  Illustrate  this.  Into 
what  two  orders  are  fishes  divided?  Are  orders  susceptible  of  still  farther  division? 
What  are  the  characteristics  of  the  mollusca  ? 


*  The  osseous  order  includes  "fishes  proper,"  whose  skeletons,  like  those  of  mam- 
malia, birds,  and  reptiles,  are  composed  chiefly  of  calcareous  earth  pervading  an  organic 
base.  The  remains  of  such  fishes  are,  therefore,  extremely  durable.  In  the  cartilaginous 
order  (sturgeons,  sharks,  etc.),  on  the  contrary,  the  skeleton  contains  scarcely  any  min- 
eral matter,  but  is  a  frame-work  of  indurated  animal  matter,  elastic,  semi-transparent, 
yielding  easily  to  the  knife,  and,  like  all  mere  animal  substances,  inevitably  subject  to  de- 
cay. The  huge  cartilaginous  skeleton  of  a  shark  will  be  lost  in  a  mass  of  putrefaction  iu 
a  few  weeks ;  while  the  bones  of  a  minute  osseous  fish  may  remain  entire  for  a  great 
length  of  time.— Hugh  Miller. 

t  "  Thus,  suppose  a  dwarf  terrier  dog  is  presented  to  us,  with  a  request  that  we  should 
indicate  its  various  titles  in  the  scheme  of  classification ;  we  begin  by  calling  it  a  verte- 
brate; we  proceed  to  assign  its  class  as  the  mammalian;  as  it  feeds  upon  flesh,  its  order 
is  obviously  that  of  the  carnivora ;  its  family  is  that  of  the  wolf,  jackal,  fox,  etc.,  named 
Canidae ;  its  genus  is,  of  course,  that  of  Canis  (dog) ;  its  species,  terrier ;  its  variety  dwarf 
terrier.  "—Lewes. 


188       FIBST     PRINCIPLES     OF     GEOLOGY. 

1.  A cephal a  (headless),  or  those  which  have  no  distinct 
heads,  and  are  inclosed  in  bivalve  shells,  as  the  oyster  and 
clam. 

2.  Gasteropoda  (belly-footed);  or  those  which  creep  upon 
a  flat  disc  or  foot,  as  the  snails. 

3.  Cephalopoda  (head-footed),  or  those  which  have  arms 
or  tentacles  arranged  about  their  mouth,  as  the  cuttle-fish, 
the  nautilus,  etc. 

As  the  different  classes  of  mollusca  lived  in  situations  favorable  to  the 
preservation  of  their  shells,  we  find  great  numbers  of  them  fossil,  and  they 
are  more  frequently  used  to  determine  the  identity  or  relations  of  strata  than 
any  other  variety  of  fossils. 

FIG.  103.  FIG.  104.  FIG.  105. 


Shells  are  either  univalve  (Figs.  103  and  104);  livalve  (Fig.  105),  or  multi- 
valve,  according  to  the  number  of  pieces  which  make  up  the  shell.  Some 
univalve  shells  are  divided  by  partitions  into  numerous  chambers,  which  are 
connected  by  a  tube  called  a  siphuncle  (see  Fig.  104),  and  are  hence  termed 
chambered  shells. 

That  branch  of  science  which  classifies  and  describes  shells  is  called  conch- 
ology. 

199.  Articulata, — Animals  of  this  sub-kingdom  have,  as 
the  name  implies,  bodies  which  are  composed  of  segments 
articulated  or  jointed  together,  as  lobsters,  crabs,  insects, 
worms,  etc. 

QUESTIONS.— Into  ho-w  many  classes  are  they  divided  ?  Enumerate  them.  What  is 
said  of  the  abundance  of  fossil  mollusca  ?  How  are  shells  of  mollusca  designated  ?  What 
are  chambered  shells?  What  is  that  branch  of  science  which  treats  of  shells  called? 
What  are  the  characteristics  of  the  articulata  ? 


CLASSIFICATION     OF     ANIMALS.  189 

The  limbs  of  articulata  are  also  jointed,  and  they  have  mostly  a  hard  cover- 
ing, which  forms  a  sort  of  external  skeleton.  Sometimes  the  segments  of 
their  body  are  numerous,  as  in  the  centiped,  lobster,  etc. ;  sometimes  several 
segments  are  fused  together,  as  in  the  crab;  and  sometimes,  as  in  worms, 
they  are  indicated  by  slight  markings,  or  depressions  of  the  skin,  which  give 
the  appearance  of  little  rings ;  and  hence  the  worms  have  been  named  anne- 
lida  or  annulata.  In  these  last-named  cases,  the  segmental  nature  of  the 
type  is  detected  in  the  fact  that  the  worms  grow  segment  by  segment ;  and 
also  in  the  fact  that  in  most  of  them  each  segment  has  its  own  nerves,  heart, 
and  stomach. 

The  articulata  have  been  divided  (Agassiz)  into  three 
classes  : 

1.  Insects,  including  spiders. 

2.  Worms. 

3.  Crustacea — lobsters,  crabs,  and  other  similar  animals. 

200.  Radiata, — This  division  of  the  animal  kingdom 
comprises  all  those  animals  whose  bodies  have  a  radiated 
or  star-like  arrangement  of  parts,  and  whose  organs  of 
sense  and  motion  are  also  circularly  disposed  around  a  cen- 
ter or  axis. 

FIG.  106. 


Many  of  the  radiata  are  fixed  as  the  coral  polyp  (see  Fig.   106,  which 
represents  a  species  of  coral,  termed,  from  its  star-like  figure,  astrcea) ;  while 

QUESTIONS.— What  is  said  of  the  construction  of  the  varieties  of  this  division  ?     How- 
many  classes  are  comprised  in  this  sub-kingdom  ?    Enumerate  them.    What  are  radiata  ? 


190       FIRST     PRINCIPLES     OF     GEOLOGY. 

others  move  and  float  about,  as  the  star-fishes  (see  Fig.  107,  which  represents 
a  fossil  species),  and  the  sea-urchins. 

"  All  the  animals  of  this  division  are  aquatic,  and  not  a  single  terrestrial 
representative  has  as  yet  been  discovered.  Only  one  species,  moreover,  is 
found  in  fresh-water." 

FIG.  107. 


The  radiata  are  arranged  in  three  classes  : 

1.  Echinoderms  (sea-urchins;  star-fish,  etc.). 

2.  Acalephs  (jelly-fish,   medusas,  etc.),  so  called  from 

their  nettling  properties. 

3.  Protozoa    (polyps,  sponges,  and  other  obscure  and' 

lowly  forms). 

These  classes,  as  in  the  other  sub-kingdoms,  are  subdivided  into  numerous 
orders,  families,  etc.,  each  having  some  peculiarity  of  structure,  growth,  or 
habit* 

201.  Classification  of  Fossil  Fishes, — Fish  are  found  in  a  fossil 
state  in  all  the  stratified  rocks,  from  the  Silurian  to  the  Tertiary  system ;  and 
from  their  number,  state  of  preservation,  and  remarkable  forms,  the  geologist 
has  been  enabled  to  deduce  many  important  inferences  respecting  the  con- 
dition of  the  surface  of  our  planet  at  the  period  of  their  existence.  As  the 
scales  or  external  coverings  are  often  the  best  preserved  portions  of  fossil 

QUESTIONS — What  are  examples  of  radiata?  Are  any  of  this  class  land  animals? 
What  are  the  divisions  of  the  radiata  ?  What  is  said  of  the  occurrence  of  fish  in  a  fossil 
state? 


*  There  is  considerable  diversity  of  opinion  among  naturalists  in  regard  to  the  classifi- 
cation of  animals  ;  the  divisions  recognized  by  some  authorities  being  much  more  minute 
than  those  adopted  by  others.  The  system  of  classification  above  given  is  substantially 
that  instituted  by  Agassiz. 


FOSSIL     FISHES. 


191 


fishes,  it  occurred  to  Prof.  Agassiz  to  arrange  them  into  orders  according  to 
the  structure  of  these  parts ;  and,  on  an  examination  of  the  subject,  he  dis- 
covered, that  there  is  always  a  relation  between  the  form  of  the  scales  of 
fishes  and  their  organization ;  and  that  this  relation,  moreover,  is  so  intimate 
and  constant,  that  if  different  species  of,  fish,  having  similar  scales,  be  com- 
pared, they  will  be  found  to  correspond  very  closely  in  their  nature  and 
structure.  * 

As  the  result  of  these  investigations,  the  class  of  fossil 
fishes  has  been  divided,  by  Agassiz,  into  four  great  orders, 
according  to  the  structure  of  their  scales,  viz.  :  1.  Pla- 
coids  ;  2.  Ganoids ;  3.  Ctenoids ;  4.  Cycloids.f 

The  characteristics  of  these  orders  are  as  follows : 

1.  Placoids  (Gr.,  7rAa£ — a  plate)  are  so  called  because  they  have  their  skin 
irregularly  covered  with  plates  of  enamel,  furnished  with  spines,  like  the 
shagreen  on  the  skin  of  a  shark.  Fig.  108,  No.  1,  represents  a  scale  from  a 
shark,  highly  magnified.  This  order  comprises  all  the  cartilaginous  fishes, 
with  the  exception  of  the  sturgeon. 

FIG.  108. 


2.  Ganoids  (Gr.,  yavo^ — splendor)  are  so  called  from  the  shining  or  en- 
amelled surface  of  their  scales.  These  scales  are  generally  angular  (see  Fig. 
108,  No.  2),  and  are  composed  of  bony  or  horny  matter,  coated  externally 
with  bright  enamel  Nearly  all  the  species  referable  to  this  order  are  extinct ; 
the  sturgeon,  and  the  gar-pike  of  the  American  lakes,  are  living  examples. 

QUESTIONS. — What  curious  discovery  has  been  made  by  Agassiz  in  relation  to  the  scales 
of  fishes  ?  How  have  fossil  fishes  been  classified  by  Agassiz  ?  What  are  the  character- 
istics of  the  Placoids  ?  Of  the  Ganoids  ? 


*  As  illustrative  of  intimate  relation  between  the  scales  of  fishes  and  their  general 
organization,  it  is  related  of  Agassiz,  that  on  one  occasion,  at  a  meeting  of  geologists,  he 
restored  the  form  of  a  then  unknown  fossil  fish,  from  the  mere  inspection  of  a  few  iso- 
lated scales  found  imbedded  in  rock ;  and  when,  after  the  lapse  of  a  considerable  period, 
a  complete  specimen  of  the  fish  in  question  was  discovered,  the  predicated  description 
was  found  to  be  correct  in  almost  every  particular. 

t  This  classification  has,  until  quite  recently,  been  made  to  embrace  all  existing  as  well 
as  all  fossil  forms  of  fishes ;  but  within  a  very  recent  period  a  more  minute  classification 
has  been  proposed  by  Prof.  Agassiz ;  for  an  explanation  of  which,  the  student  is  referred 
to  his  "  Essay  on  Classification,"  page  1ST  (1857). 


192       FIRST     PRINCIPLES     OF     GEOLOGY. 

3.  The  Ctenoids  (Or.,  KTELS — a  comb)  have  horny  scales,  without  enamel, 
and  serrated  on  the  posterior  edge,  like  the  teeth  of  a  comb.     (See  Fig.  108, 
No.  3.)    The  perch  may  be  taken  as  a  living  example  of  this  order. 

4.  The   Cyloids  (Gr.,  Ki>/cAo?— a  circle)  have  smooth  scales,  also  without 
enamel,  which  are  entire  or  rounded  .at  their  margins.     (See  Fig.  108,  No.  4.) 
The  herring,  trout,  and  salmon  are  living  examples  of  this  order,  which  em- 
braces the  majority  of  existing  species. 

202.  Fish  have  also  two  distinctive  forms  of  tail ;  and 
may  be  arranged  in  two  classes,  heterocercals  and  homocer- 
cals,  according  as  their  tails  are  equally,  or  unequally  lobed. 

Thus,  in  heterocercal  species,  the  tail  is  chiefly  on  one  side,  like  that  of  the 
shark  and  sturgeon  (Fig.  109),  the  backbone  being  prolonged  into  the  upper 
lobe ;  in  homocercal  species,  the  lobes  of  the  tail  are  equal  and  similar,  as  in 
the  trout,  perch,  etc.  (See  Fig.  110.) 

Fio.  109.  FIG.  110. 


In  palaeontology  this  distinction  is  a  very  important  one ;  inasmuch  as  it 
has  been  found  that  all  the  fishes  which  lived  during  the  earlier  ages  of  the 
earth's  history,  or,  to  speak  more  precisely,  all  those  whose  remains  are  found 
fossil  in  strata  older  than  the  Triassic  system  had  heterocercal  or  unequaDy' 
lobed  tails  ;  while  the  great  majority  of  those  found  fossil  in  more  recent 
strata,  and  existing  at  the  present  day,  have  symmetrical  or  homocercal  tails. 

203.  Besides  those  distinctions  which  depend  on  the  structure  and  form 
of  animals  and  plants,  there  are  others  of  importance  constantly  recognized 
by  the  geologist  and  naturalist,  which  depend  on  climate,  habitat,  and  mode 
of  life. 

Adaptation  of  Organization  to  Condition. — Each  race 
of  plants  and  animals  is  perfectly  adapted  by  the  Crea- 
tor for  the  functions  it  has  to  perform  in  the  economy  of 
nature  ;  and  is  furnished  with  peculiar  organs,  according 
to  the  kind  of  food  upon  which  it  lives  and  the  habits  it 
displays. 

QUESTION.— What  are  the  characteristics  of  the  Ctenoids  ?  Of  the  Cycloids?  What  is 
said  of  the  forms  of  tails  of  fishes  ?  When  are  fishes  said  to  have  hetrocercal  tails  ? 
When  homocercal  ?  Besides  form  and  structure,  what  other  distinctions  between  ani- 
mals and  plants  are  recognized  ?  What  is  said  of  the  adaptation  of  animals  and  plants  to 
their  condition  ? 


DISTRIBUTION    OF    PLANTS    AND    ANIMALS.     193 

Thus,  one  set  of  organs  indicates  swiftness;  another  strength;  a  third, 
prehensile  or  seizing  powers  ;  a  fourth,  climbing,  leaping,  or  swimming 
powers ;  and,  a  fifth,  that  the  animal  lives  on  roots,  on  herbage,  or  on  the 
flesh  of  others. 

Furthermore,  all  the  parts  of  animals  or  plants  sustain, 
a  definite  relation  to  each  other.  This  law  was  first  stated 
by  the  great  naturalist,  Cuvier,  in  the  following  terms  : 

"Every  organized  being  forms  a  whole — a  complete 
system— *all  the  parts  of  ivhich  mutually  correspond. 
None  of  these  parts  can  change  without  the  others  also 
changing ;  and,  consequently,  each  taken  separately,  indi- 
cates and  gives  all  the  others." 

For  example,  the  sharp-pointed  tooth  of  a  lion  requires  a  strong  jaw ;  a 
skull  fitted  for  the  attachment  of  powerful  muscles,  both  for  moving  the  jaw 
and  raising  the  head ;  a  broad,  well-developed  shoulder-blade ;  an  arrange- 
ment of  the  bones  of  the  fore-leg  which  admits  of  the  leg,  with  the  paw,  being 
rotated,  and  turned  upward,  by  which  its  application  as  a  seizing  and  tear- 
ing instrument  is  greatly  increased ;  and  a  paw  armed  with  strong  claws. 
On  the  other  hand,  teeth  adapted  for  bruising  and  grinding,  but  not  for  tear- 
ing food  (as  the  teeth  of  the  ox,  and  like  animals  which  feed  upon  herbage), 
are  connected  with  a  peculiarly  shaped  skull,  blade- bone,  fore-leg,  and  hoofed 
foot.  So  that,  if  we  possess  but  a  single  tooth,  or  any  other  characteristic 
part  c/f  an  animal,  it  is  quite  possible  to  pronounce  with  certainty  upon  the 
general  form  and  habits  of  the  animal  to  which  it  belonged. 

204.  Distribution  of  Plants  and  Animals,— The  distri- 
bution of  animals   and  plants  is  twofold — vertical   and 
lateral. 

205.  Both  on  land  and  in  water,  animals  and  plants 
vary  as  we  depart  upward  or  downward  from  the  level  of 
the  sea. 

"We  are  all  familiar  with  this  variation  on  the  land — every  one  being  aware 
that  vegetation  undergoes  a  greater  change  in  ascending  vertically  upward 
from  the  level  of  the  sea,  up  the  sides  of  a  lofty  mountain  to  the  regions  of 
perpetual  snow,  than  it  does  in  traveling  laterally  toward  the  pole  till  we 
reach  the  point  where  perpetual  snow  comes  down  to  the  sea-level ;  and  with 

QTHEBTIONB. — Do  all  the  parts  of  an  animal  structure  sustain  a  relation  to  each  other? 
What  law  was  expressed  by  Cuvier?  Show  by  examples  how  all  the  parts  of  an  animal 
are  related.  What  is  said  of  the  distribution  of  plants  and  animals  ?  How  do  plants  and 
animals  vary  as  we  depart  from  the  level  of  the  sea? 


194       FIRST     PRINCIPLES     OF     GEOLOGY. 

a  change  in  vegetable  life,  an  equal  change  in  animal  life  is  a  necessary  con- 
sequent effect  in  all  regions  of  the  globe. 

The  climates  of  the  sea  vary  more  rapidly  in  depth  than  those  of  the  land 
do  in  height ;  since  the  light  and  heat  of  the  sun — the  great  vivifying  prin- 
ciples of  nature — lose  all  influence  at  the  depth  of  a  very  few  hundred  feet 
into  the  ocean,  even  under  the  tropics,  where,  in  the  air,  life  ranges  through 
a  vertical  zone  of  16,000  feet.  The  level  of  the  sea,  and  a  few  feet  above  and 
below  it,  is  the  populous  film  of  the  earth ;  departing  from  that  film  in  either 
direction,  living  beings  rapidly  become  less  numerous,  and  shortly  disappear. 

206.  "With  the  lateral  distribution  of  terrestrial  life,  all  persons  are  more  or 
less  familiar.  We  know,  for  instance,  that  plants,  such  as  the  vine,-  the  Kpple, 
the  banana,  the  cocoa-nut,  rice,  wheat,  oranges,  etc.,  do  not  grow  indiscrimi- 
nately wherever  they  may  be  planted ;  they  are  confined  to  certain  portions 
of  the  globe,  where  the  climate  is  suitable  for  them.  We  know,  also,  that 
the  polar-bear  and  the  lion,  the  reindeer  and  the  camel,  the  musk  ox  and 
the  giraffe,  could  not  exchange  habitats,  and  could  not,  in  a  wild  state,  in- 
habit the  same  countries. 

The  inhabitants  of  the  ocean  are,  in  like  manner,  similarly  confined  within 
certain  definite  boundaries.  Each  coast  and  sea  has  animals  which  are 
peculiar  to  it.  Of  the  200  species  of  molluscs  living  on  the  coast  of  New 
England,  fifty  are  never  found  north  of  Cape  Cod,  and  over  eighty  are  never 
found  south  of  the  Cape. 

207.  From  these  natural  provinces,  or  districts,  animals 
and  plants,  with  few  exceptions,  never  wander ;  and  when 
forced  to  remove,  do  not  long  endure  the  differences  of  cli- 
mate, food,  and  other  changes  to  which  they  are  subjected.'-' 

QTTESTIONS. — "What  are  illustrations  of  this  fact  ?  What  is  said  of  the  climate  of  the 
ocean  ?  What  zone  of  the  earth  is  most  densely  populated  ?  What  is  said  of  the  lateral 
distribution  of  terrestrial  life  ?  What  of  marine  life  ?  What  are  some  examples  of  the 
geographical  limitation  of  species?  Do  animals  and  plants  naturally  wander  from  their 
peculiar  province  ? 

*  The  information  which  has  been  collected  upon  this  subject  is  exceedingly  curious 
and  interesting.  Thus,  the  mammals  found  upon  the  great  island  continent  of  Australia 
are  all  "pouched"  animals,  like  the  opossum,  kangaroo,  etc.,  known  as  an  order  by  the 
name  of  Marsupials.  It  is  also  stated,  that  with  a  single  exception,  there  is  no  species  of 
mammal  found  in  Eastern  Australia  that  lives  in  the  western  portion  of  this  great  island. 
Even  with  regard  to  birds,  creatures  whose  powers  of  easy  and  rapid  locomotion  seem 
to  place  the  whole  world  at  their  disposal,  we  find  the  same  restriction  in  their  geo- 
graphical boundaries,  which  they  rarely  or  never  overstep.  The  "  lammergeyer"  (a 
species  of  vulture)  is  found  only  amid  the  Alps;  and  the  condor  dwells  only  amid  the 
Andes  of  South  America.  "We  might  sail  round  the  world  in  th%latitude  of  the  Cape 
of  Good  Hope,  or  thereabouts,  ever  surrounded  by  flights  of  albatrosses  and  cape-pigeons, 
which  seem  sometimes  to  people  the  air ;  but  if  the  navigator  turns  his  vessel  toward  tho 
north  he  soon  reaches  a  latitude  where  all  these  creatures  disappear.  This  takes  place 
Rot  gradually,  but  at  once.  The  ship  may  be  surrounded  by  the  usual  flocks  at  night, 
&nd  the  next  morning  not  one  of  them  will  be  seen,  or  ever  after,  till  the  navigator  re- 
turns to  the  line  where  they  left,  and  then  he  finds  fresh  flocks,  as  if  awaiting  his  arrival." 


WHAT     IS     A     SPECIES?  195 

A  few  species  of  animals  and  plants,  however,  seem  capable  of  adapting 
themselves  to  all  climates,  and  range  over  the  whole  earth.  Among  animals, 
this  is  especially  true  of  man,  and  the  dog. 

208.  From  these  statements,  the  student  will  readily  understand  h'ow  the 
geologist  is  able,  by  comparison  and  analogy,  to  decide  as  to  the  character  of 
the  fossil  animals  and  plants  which  he  discovers ;  and  how  he  can  tell,  with 
precision,  whether  they  lived  in  the  waters  or  on  dry  land ;  in  fresh  or  salt 
water ;  in  a  cold  or  hot  climate ;  whether  the  animals  fed  upon  plants  or 
lived  upon  other  animals  ;  whether  they  are  furnished  with  organs  indicating 
an  amphibious  existence  ;  and,  in  general,  he  can  determine  their  nature  and 
modes  of  existence.     Moreover,  as  certain  classes  of  plants  and  animals  indi- 
cate certain  conditions  of  the  earth's  surface,  the  geologist  is  enabled,  by  tho 
study  of  their  remains,  to  decipher  the  past  history  of  our  globe,  and  so  arrive 
at  results  which,  at  first  thought,  seem  hopelessly  beyond  the  grasp  of  the 
human  intellect. 

209.  Number  of  Species  in  the  Animal  and  Vegetable 
Kingdom, — The  number  of  species  of  animals  now  living 
upon  the  surface  of  the  earth,  is  estimated  at  about  250,000. 

What  is  a  Species? — A  species  maybe  defined  to  be  a 
kind  of  animal  or  plant,  so  distinct  from  all  others  that 
the  continuation  of  the  "kind,"  or  species,  is  possible  only 
between  a  pair  belonging  to  that  species.  In  other  words, 
the  individuals  of  a  species  may  be  regarded  as  the  de- 
scendants of  a  single  pair,* 

210.  The  number  of  species  of  vertebrate  animals  is  estimated  at  about 
20,000,  divided  as  follows:   1,500  to  2,000  species  of  mammalia;   5,000  to 
6,000  species  of  birds;  1,500  to  2,000  of  reptiles;  and  from  8,000  to  10,000 
offish. 

211.  The  number  of  species  of  molluscs  already  in  collections  (museums) 
probably  exceeds  20,000  ;  there  are  collections  of  marine  shells,  bivalve  and 
univalve,  which  have  over  19,000  species;    and  collections  of  land  and  fresh- 
water shells,  which  count  as  many  as  2,000. 

QUESTIONS. — What  use  are  all  these  facts  in  natural  history  to  the  geologist  ?  What 
is  the  estimated  number  of  species  of  animals  and  plants  now  living?  What  is  a  species  ? 
What  is  said  of  the  number  of  living  vertebrate  animals  ?  Of  molluscs  ? 


*  Offspring  cannot  be  produced  by  a  pair  of  individuals  of  different  species,  except  when 
those  individuals  are  very  nearly  allied  to  each  other,  and  even  then  the  progeny  (termed 
a  hybrid),  it  is  said,  can  never  be  perpetuated;  thus  clearly  showing  "that  nature  re- 
pudiates such  amalgamations,  and  keeps  her  species  jealously  distinct  and  invariable." 
For  example :  the  horse  and  the  ass  belong  to  the  same  genus,  and  although  allied  to 
each  other  in  many  respects,  yet  belong  to  different  species.  The  progeny  of  the  two 
species  is  a  mule— a  hybrid— partaking  of  the  qualities  of  both  the  horse  and  the  ass. 
But  mules  do  not  propagate  their  kind. 


196        FIRST     PRINCIPLES     OF     GEOLOGY. 

212.  The  number  of  species  of  articulata  (worms,  insects,  Crustacea,  etc.) 
has  been  estimated  at  200,000.    There  are  collections  of  coleopterous  (beetles) 
insects  alone  which  number  25,000  species. 

213.  The  number  of  species  included  in  the  division  of  radiata  (the  star-" 
fishes,  medusae,  polypi,  etc.)  has  been  estimated  as  at  least  10,000. 

The  number  of  species  of  plants  now  living  upon  the  earth  has  been  sup- 
to  be  150,000. 


214.  Number  of  Fossil  Species  of  Animals  and  Plants, 
— No  reliable  estimate  can  be  made  of  the  number  of 
species  of  animals  and  plants  existing  in  a  fossil  state  ; 
but  it  is  safe  to  say,  that  the  sum  total  exceeds  many  times 
the  number  of  all  the  species  now  living. 

Thus,  a  deposit  of  limestone  in  the  neighborhood  of  Paris,  France,  which  is 
merely  one  division  of  one  of  the  four  groups  of  strata  included  in  the  tertiary 
system,  contains  not  less  than  1,200  species  of  fossil  shells ;  whereas  the  species 
now  living  in  the  Mediterranean  Sea  do  not  amount  to  half  that  number. 
Similar  relations  may  be  also  pointed  out  in  America ; — 
Thus,  there  have  been  described  from  the  so-called  "  Trenton  limestone"  of 
New  York  (one  of  the  stratified  deposits  that  belong  to  the  Silurian  system 
of  that  State),  170  species  of  fossil  shells — a  number  almost  equal  to  that  of 
all  the  species  now  found  living  on  the  coast  of  Massachusetts.'31' 

215.  The  number  of  individuals  included  in  the  several 
fossil  species,  moreover,  was  not  less  than  is  comprised  by 
existing  species. 

In  thousands  of  localities  in  the  State  of  New  York,  and  throughout  the 
Valley  of  the  Mississippi,  the  great  bulk  of  the  rocks  may  be  seen  to  be 
almost  entirely  formed  of  animal  remains,  particularly  corah  and  shells. 
Fig.  Ill  represents  a  limestone  found  near  Lockport,  N.  Y.,  which  is  almost 
wholly  composed  of  the  remains  of  radiated  animals,  known  as  crinoids  or 

QUESTIONS. — What  is  said  of  articulata  ?  Of  radiata  ?  What  is  said  of  the  number  of 
fossil  species  of  animals  and  plants  ?  What  facts  prove  the  great  abundance  of  'extinct 
fossil  species?  What  is  said  of  the  number  of  individuals  included  ia  the  fossil  species  ? 


*  The  stratified  rocks  of  Great  Britain  have  probably  been  studied  more  minutely  than 
those  of  any  other  equal  area  of  the  earth's  surface,  and  as  the  result  of  these  investiga- 
tions it  has  been  found — that  the  number  of  species  of  extinct  mammalia,  contained  in  the 
fossiliferous  rocks  of  the  British  islands,  is  more  numerous  by  one  half  than  all  the  species 
now  existing  there ;  of  molluscs,  the  fossil  species  are  nine  times  as  numerous  as  the 
living  species;  the  fossil  fish  five  times;  the  reptiles  ten  times;  and  the  radiata  at  least 
fourteen  times.  In  instituting  such  a  comparison,  moreover,  it  should  be  remembered 
that  while  the  existing  population  is  almost  entirely  known  from  recent  elaborate  re- 
searches, we  arc  as  yet  only  imperfectly  acquainted  with  the  extinct  fossil  races. 


NUMBER     OF     FOSSILS.  197 

stone-lilies; — Fig.  29  exhibits  the  structure  of  the  animal  entire.  Now,  if  we 
consider  the  slowness  with  which  corals  and  shells  are  formed,  it  will  give 
us  some  idea  of  the  vast  series  of  ages  that  must  have  elapsed  in  order  to 
allow  of  the  formation  of  these  rocks,  and  their  regular  deposition  under 
•water,  to  so  great  a  thickness. 

FIG.  111. 


Fossils  occur  abundantly,  not  only  in  rocks  at  great  depths  below  the 
present  surface  of  the  earth,  but  also  in  the  rocks  that  constitute  the  highest 
mountains  of  the  globe.  In  Switzerland,  a  large  part  of  some  of  the  moun- 
tains of  the  Jura  is  composed  of  fossil  corals.  Tn  the  Alps  and  Pyrenees, 
the  rocks,  to  a  height  of  6,000  to  8,000  feet  above  the  level  of  the  sea, 
abound  in  marine  fossils — shells,  corals,  etc. ;  and  in  the  Andes  and  Hima- 
layas, they  are  found  at  a  height  of  from  16,000  to  20,000  feet. 

216.  Furthermore,  of  the  hundreds  and  thousands  of 
species  of  animals  and  plants  found  fossil  in  the  strati- 
fied rocks  which  were  formed  before  the  epoch  of  the  Ter- 
tiary system,  not  one  has  ever  been  proved  to  be  identical 
with  any  animal  or  plant  now  living. 

"  The  dust  wo  tread  upon  was  once  alive," 

is  thus  proved,  by  the  researches  of  the  geologist,  to  be  no 
poetical  exaggeration. 

217.  Causes  of  the  Extinction  of   Species, — Every  extensive 
area  of  the  earth's  surface  that  has  yet  been  examined  bears  unmistakable 
evidence  of  having  been  subjected  to  successive  great  geological  changes : 

QUESTIONS.— Illustrate  this.  What  is  said  of  the  distribution  of  fossils  ?  What  facts 
illustrate  this  ?  Are  the  species  found  fossil  the  same  as  those  now  living  ?  What  fact  is 
true  of  every  area  of  the  earth's  surface  thus  far  examined  geologically? 


198      FIRST     PRINCIPLES      OF     GEOLOGY. 

i.  e.,  of  having  been  alternately  sea-bottoni  and  dry  land.  "With  each  of 
these  changes,  it  is  obvious  that  all  existing  forms  of  life  comprised  within 
the  area  affected,  must  have  perished;  leaving  their  various  remains  imbedded 
in  stratified  deposits,  to  testify  of  their  existence. 

In  such  alternations  of  the  earth's  surface,  and  in  the  changes  of  climato 
that  must  necessarily  have  accompanied  thern^the  geologist  finds  sufficient 
explanation  of  the  extinction  of  the  races  of  animals  and  plants  .that  in- 
habited our  earth  during  former  geological  periods.  There  may  have  been 
other  causes  which  contributed  to  such  results,  such  as  epidemic  diseases, 
the  introduction  of  hostile  races  of  animals,  volcanic  emanations,  and  the 
like;  but  these  last  must  have  been  more  or  less  local  in  their  influence.* 


CHAPTER     XI. 

HISTORY    OF    THE   FORMATION  OF    THE  SYSTEMS    OF    THE 
STRATIFIED  ROCKS. 

218.  A  CAREFUL  consideration  of  the  statements  presented  in  the  preceding 
chapters  will  have  prepared  the  student  now  to  commence  intelligently  the 
study  of  the  history  of  the  formation  of  the  several  great  systems  of  stratified 
rocks ;  or,  in  other  words,  the  history  of  our  earth  and  of  the  life  upon  its  sur- 
face during  the  successive  epochs  of  time  when  the  several  great  divisions  of  the 
stratified  rocks  were  in  the  process  of  formation. 

This-  history  may  be  presented  in  two  ways ;  namely,  by  investigating,  or 
tracing  it  backwards,  from  the  present  to  the  past ;  or  by  narrating  it  as 
nearly  as  possible  in  the  order  in  which  it  occurred.  The  latter  method  is 
preferred  as  the  most  intelligible,  and  as  being  also  in  conformity  with  the 
manner  in  which  history  in  general  is  studied. 

"As,  however,  to  present  this  history  in  fall,  even  so  far  as  already  known, 
would  require  a  library  rather  than  a  book,  what  will  be  here  given  must  be 
taken  as  a  mere  abstract — a  chronological  table — rather  than  a  history,  by 
means  of  which  the  student  will  be  able  to  refer  to  its  proper  place  every 
detailed  account  (which  he  may  either  read  or  observe  for  himself)  of  its 
different  portions." 

219.  What  are  the  Oldest  Rocks?— Kegarding  the  for- 
mation of  the  rocks  which  compose  the  crust  of  the  earth 

QUESTIONS. — What  causes  are  assigned  by  geologists  for  the  extinction  of  species? 
What  subject  in  order  comes  next  under  consideration?  In  what  order  may  the  history 
of  the  stratified  rocks  be  presented  ?  What  question  of  interest  presents  itself  in  this 
connection  ?  v 

*  In  1842,  a  large  proportion  of  the  molluscs  on  the  shores  of  Northern  Australia  were 
suddenly  exterminated  by  some  apparently  rapidly  contagious  disease. 


THE     OLDEST      ROCKS.  199 

as  the  result  of  successive  processes,  the  question  naturally 
suggests  itself :  What  were  the  first  formed  rocks  ?  or, 
What  are  the  oldest  rocks  of  which  we  possess  any  posi- 
tive information  ? 

If  we  accept  the  supposition  that  tho  entire  mass  of  our  earth  was  at  one 
period  of  its  history  in  a  molten  fluid  condition  (see  §  133),  then  the  first 
formed  rocks  were  the  product  of  the  cooling  and  consolidation  of  the  planet's 
exterior. 

Concerning  the  nature  of  this  primeval  crust,  we  have  probably  no  posi- 
tive information.  The  general  opinion  of  geologists  at  the  present  day  is, 
that  no  part  of  it  is  now  in  existence,  and  that  none  of  the  rocks  now  open 
to  observation  can  date  back  their  formation  to  this  pre-historic  or  pre- 
geologic  epoch  of  the  earth's  duration. 

"  Whatever  may  have  been  the  nature  of  this  primeval  crust  of  the  globe," 
says  Prof.  Ramsay,  "  it  must  have  been  more  or  less  completely  destroyed 
and  remodeled  by  the  erosive  action  of  water,  and  the  remelting  action  of 
heat,  long  before  the  commencement  of  even  the  earliest  of  our  geological 
periods."  % 

The  variety  or  type  of  rock  open  to  our  observation, 
generally  believed  to  be  the  oldest,  is  granite. 

,  The  principal  evidence,  which  induces  this  belief,  is  derived  from  the  fact, 
that  in  all  parts  of  the  globe,  wherever  the  base  of  the  aqueous  or  stratified 
rocks  has  been  upheaved  to  the  surface  and  thus  exposed  to  view,  that  base 
has  been  found  to  rest  upon  granite*  "And  we  have  every  reason,  moreover, 
to  believe, "  says  Mr.  Jukes,  "  that  if  we  could  penetrate  the  crust  of  the 
earth,  at  any  part  of  its  surface,  vertically,  to  a  sufficient  depth,  wo  should 
in  all  cases,  eventually  encounter  granite,  and  find  it  to  be  the  final,  under- 
lying material.''!  The  structure  of  granite,  and  its  occurrence  as  an  eruptive 
rock — i.  e.,  in  veins,  dikes,  etc. — is  also  evidence  that  it  has  been  formed  en- 
tirely or  in  part  through  the  agency  of  heat. 

QUESTIONS. — According  to  the  theory  of  the  former  molten  fluidity  of  the  earth,  what 
•were  the  first  formed  rocks  ?  What  information  have  we  concerning  the  primaeval  crust 
of  the  earth?  Is  any  part  of  it  probably  in  existence  ?  What  type  or  variety  of  rocks  is 
generally  believed  to  be  the  oldest  ?  What  facts  lead  to  this  inference  ? 


*  By  the  "base  of  the  aqueous  rocks"  is  meant  the  lowest  aqueous  or  sedimentary 
rocks  known  in  the  particular  locality,  whatever  may  be  their  age,  and  not  necessarily 
the  absolutely  oldest  aqueous  rocks. 

t  By  some  geologists  the  universality  of  this  proposition  has  been  questioned.  (See 
paper  on  "  The  Theory  of  the  Transformation  of  the  Sedimentary  Deposits  into  Crystal- 
line Rocks,"  by  T.  S.  Hunt.  Jour.  Geological  Society,  London.  1859.  pp.  488-496 ; 
also  Annual  Scientific  Discovery,  1860.  pp.  304-811.)  The  affirmative  is,  however, 
maintained  by  Mr.  Jukes,  at  present  one  of  the  directors  of  the  Geological  Survey  of 
Great  Britain,  and  by  other  leading  authorities. 


200        FIRST     PRINCIPLES     OF     GEOLOGY. 


These  facts,  therefore,  led  geologists  at  one  time  almost  universally  to  sup- 
pose that  granite,  wherever  found  at  the  surface  of  the  earth,  was  always  the 
oldest  of  the  rocks,  and  in  reality  represented  a  part  of  the  original  primeval 
crust  of  the  globe.  But  these  views  are  at  present,  however,  wholly  aban- 
doned, since  it  is  now  known  that  intrusive  masses  of  granite  penetrate  and 
overlie  rocks  which  have  been  formed  during  almost  every  period  of  the  earth's 
history. 

FIG.  112. 


When  granite  also  forms,  as  it  frequently  does,  the  nucleus  or  axis  of 
mountain  masses,  the  stratified  rocks  which  rest  up on  the  flanks  of  the  moun- 
tain dip  from  the  granite  in  every  direction,  as  is  represented  in  Pig.  112  ; 
thus  conclusively  proving,  that  the  period  of  the  elevation  of  the  granite,  and 
the  formation  of  the  mountain,  was  subsequent  to  the  deposition  of  the  most 

recent  of  the  strata  that  have  been  disrupted  by  it.* 

• 

While  granite,  therefore,  is  undoubtedly,  in  many  cases, 
the  oldest  and  lowest  in  position  of  all  known  rocks,  it  is' 
not  invariably  so  ;  and  its  relative  age  in  all  cases  can  only 
be  inferred  from  the  age  of  the  stratified  rocks  with  which 
it  is  associated. 

Furthermore,  if  we  adopt  the  generally  received  hypothesis,  that  all  the 
materials  of  the  earth,  at  a  certain  depth  in  its  interior,  are  in  a  state  of 
fusion,  it  is  probable  that  granite  is  even  now  in  the  process  of  formation, 
wherever  molten  mineral  matter  of  the  proper  chemical  composition  is  con- 
solidating under  the  requisite  physical  conditions. 

220.  If  we  are  inclined  to  speculate  on  the  character  of  the  material  which 
would  result  from  the  cooling  of  the  crust  of  a  molten  globe,  we  may  reason- 

QUESTIONS.— To  what  conclusions  -were  the  earlier  geologists  led  respecting  granite  ? 
Is  granite  always  the  oldest  rock?  What  facts  prove  that  it  is  not  ?  What  is  said  con- 
cerning its  relative  age  ? 


*  In  Fig.  112,  G  represents  a  mass  of  granite  forming  the  axis  of  a  range,  and  1,  2,  3, 
stratified  rocks,  dipping  from  it  in  each  direction ,  the  eldest  or  lowest,  No.  1,  being  next 
to  the  granite,  and  highest,  or  newest,  No.  3,  the  farthest  from  it.  Now,  as  the  strata 
1,  2, 3  must  have  heen  deposited  in  a  nearly  horizontal  position,  it  is  clear  that  the  granite' 
G,  was  not  intruded  until  after  the  deposition  of  N.  3  on  the  top  of  No.  1  and  2. 


STRATIFIED     BOCKS.  201 

ably  doubt  the  possibility  of  the  formation  of  so  dense  a  rock  as  granite  on 
a  surface  where  the  expansive  power  of  heat  must  have  acted  with  the  great- 
est intensity.  (See  §  45.)  Mr.  T.  S.  Hunt,  of  the  Canadian  Geological 
Survey,  inclines  to  the  opinion  that  the  primitive  rock  must  have  rather 
resembled  a  variety  of  trap  (dolerite) ;  while  other  geologists  have  supposed 
that  it  had  the  character  of  porous  trachyte,  pumice,  or  obsidian  (volcanic 
glass).  (See  §30.)* 

But  however  this  may  be,  the  granitic  rocks  may  be  assumed  to  consti- 
tute the  basis  upon  which  the  stratified  rocks  rest.  "We  know,  also,  that  the 
agencies  which  produced  granite  in  the  first  instance  continued  to  operate 
during  the  formation  of  all  the  systems  of  the  stratified  rocks  as  high  up  in 
the  series  as  (and  including)  the  Tertiary  system. 

221.  Relation  of  the  Unstratified  or  Igneous  Rocks  to 
the  Different  Systems  of  Stratified  Rocks,— The  general  re- 
lation and  position,  which  the  three  classes  of  igneous  rocks  (granitic,  trap- 
pean,  and  volcanic)  sustain  to  the  different  systems  of  the  stratified  rocks, 
may  be  briefly  indicated,  as  follows : 

Intrusive  masses  of  granite  are  found  most  abundantly  associated  with  the 
stratified  rocks  of  the  Azoic  period,  and  with  the  older  systems  and  groups 
of  the  Paleozoic  period.  The  great  epoch  of  the  eruptive  intensity  of  granite 
would  seem  to  have  terminated  with  the  deposition  of  the  rocks  of  the  Silu- 
rian and  Devonian  systems,  and  its  occurrence  in  the  succeeding  systems 
must  be  considered  as  exceptional.  In  Great  Britain  granite  veins  are  found 
traversing  rocks  of  the  Carboniferous  and  Triassic  systems ;  and  in  the  Alps 
and  in  Southern  Italy  granitic  outbursts  and  upheavals  are  associated  with 
strata  of  the  Cretaceous  and  Tertiary  systems.  No  eruption  of  granite  is 
believed  to  have  taken  place  withia  the  Recent  or  Historic  period. 

Eruptions  of  trappean  rocks  took  place  most  abundantly  in  the  Mesozoic 
period,  especially  in  the  Triassic  and  Oolitic  systems;  and  also  in  the  Terti- 
ary system  of  the  Cainozoic  period ;  while  to  all  igneous  rocks  which  have 
erupted  during  the  recent  or  present  epoch  wo  apply  the  name  Volcanic.  It 
is,  however,  almost  impossible,  as  has  been  before  remarked,  to  recognize 
any  very  clear  distinction  between  some  volcanic  lavas  and  certain  of  the 
more  ancient  traps.  (See  §  38.) 

QUESTIONS. — What  was  probably  the  nature  of  the  first  formed  rocks  ?  What  may  we 
assume  as  the  bases  of  the  stratified  rocks  ?  With  which  of  the  systems  of  stratified  rocks 
is  granite  found  most  abundantly  associated?  How  high  up  in  the  series  does  it  occur? 
In  what  sysems  do  the  trap  rocks  occur  most  abundantly  ?  In  what  the  volcanic  ? 

*  If  we  accept  the  theory  that  slow  cooling  and  enormous  pressure  are  the  necessary 
and  concomitant  conditions  for  the  formation  of  granite,  it  may  be  questioned  if  it  was 
ever  formed  at  or  near  the  immediate  surface  of  the  earth ;  since  molten  rock,  that  once 
reached  or  came  near  the  surface,  and  consequently  cooled  under  normal  conditions, 
would  not  form  granite,  but  some  other  variety  of  igneous  rock,  such  as  trap  or  lava. 
Some  geologists,  furthermore,  who  adopt  this  theory  of  the  deep-seated  origin  of  granite, 
maintain,  that  wherever  we  find  granite  forming  the  present  surface  of  the  earth  we  may 
be  sure,  that  at  the  time  of  its  consolidation,  it  was  covered  with  great  masses  of  other 
rocks  (possibly  thousands  of  feet  in  thickness),  and  that  these  have  been  since  swept  off 
and  removed  by  the  action  of  water. 


202       FIRST     PRINCIPLES     OF     GEOLOGY. 


BOCKS     OF      THE      AZOIC      PERIOD.  203 

Fig.  AA,  which  represents  an  ideal  section  of  the  earth's  crust,  illustrates 
the  manner  in  which  the  three  classes  of  igneous  rocks,  erupted  from  below, 
penetrate  and  distribute  themselves  throughout  the  various  systems  of  the 
stratified  rocks. 


STRATIFIED  ROCKS   OF  THE  AZOIC  PERIOD. 

222.  The    First    Formed    Stratified    Rocks, — The  adoption  of 
the  theory,  that  our  earth  was  once  in  a  state  of  entire  molten  fluidity,  in- 
volves the  existence  of  a  subsequent  period,  when  its  primeval  crust  had 
sufficiently  cooled  down  to  allow  of  the  condensation  of  watery  vapor  and  of 
the  existence  of  a  sea  upon  its  surface.     Whenever  this  happened,  the  erod- 
ing and  destructive  action  of  water  must  have  immediately  manifested  itself, 
while  the  particles  of  the  consolidated  igneous  crust,  worn  off  by  the  action 
of  waves,  tides,  and  currents,  and  deposited  as  sediments,  would  naturally 
produce  stratified  formations. 

The  internal  heat  of  the  earth  at  that  period,  however,  must  have  con- 
tinued to  act  with  great  intensity  near  the  surface,  and  the  strata  first  de- 
posited, consequently,  were,  in  all  probability,  soon  greatly  metamorphosed, 
*.  e.,  remelted  down  to  form  igneous  rocks,  or  converted  into  hard,  crystalline, 
semi-igneous  rocks,  that  retained,  in  part,  their  .original  lines  of  stratification. 

Whether  any  of  these  first  formed  stratified  rocks  are  in  existence,  and 
open  to  our  inspection,  it  is  impossible  to  -affirm.  Some  geologists  incline  to 
the  opinion  that  they  were  entirely  re-melted,  and  are  now  represented  by 
the  older  or  fundamental  granites,  which,  in  some  instances,  appear  to  have 
an  obscurely  stratified  structure. 

Be  this  as  it  may,  it  is,  however,  a  matter  of  fact,  that  the  oldest  rocks  of 
which  we  have  any  knowledge,  which  exhibit  evidence  of  -a  sedimentary 
origin,  appear  to  have  been  formed  under  conditions  analogous  to  those  above 
supposed.  Thus,  they  are  ah1  more  or  less  crystalline  and  indurated ;  their 
lines  of  stratification  are  indistinct,  and  often  altogether  obliterated;  and 
their  whole  aspect  is  very  different  from  what  is  usually  ascribed  to  rocks 
deposited  in  water.  • 

223.  Geologists  are  not  fully  agreed  as  to  the  order  of  succession  of  the 
several  varieties  of  these  primitive  stratified  rocks,  or  as  to  the  manner  in 
which  they  may  be  best  arranged,  or  divided  into  groups  or  systems — the 
whole  formation  being  of  immense  thickness,  and  imperfectly  explored.     As 
regards  the  order  of  succession  of  rock  varieties,  it  may,  however,  be  received 
as  a  general  truth,  that  gneiss,  or  rocks  of  a  gneissic  character,  occupy  the 
lowest  position,  or  constitute  the  base  of  the  series  of  stratified  rocks.     In 

QUESTIONS.— Under  what  circumstances  is  it  inferred  that  the  first  sedimentary  rocks 
were  deposited  ?  Are  any  of  these  rocks  supposed  to  be  in  existence  ?  What  are  their 
characteristic  features  of  the  oldest  stratified  focks  known  to  us  ?  In  what  manner  do 
the  varieties  of  these  older  rocks  succeed  each  other? 


204      FIRST     PRINCIPLES     OF     GEOLOGY. 

many  instances,  this  gneiss  can  hardly  be  distinguished  from  granite,  arid 
sometimes  undoubtedly  passes  into  it. 

Succeeding  the  gneiss,  and  resting  upon  it,  we  have  groups,  or  deposits, 
of  schistose  rocks — i.  e.,  hornblende-schist,  talcose-schist,  mica-schist  or  slate — 
occurring  in  about  the  order  named;  with  formations  of  crystalline  or  meta- 
morphic  limestones,  serpentine,  and  steatite  ;  while  above  them,  we  find  quartz 
rocks  and  argillaceous  or  clay-slates.* 

Of  this  series,  the  gneiss  at  the  bottom,  thb  mica-schists  occupying  an  in- 
termediate position,  and  the  clay-slates  at  or  near  the  top,  are  the  rocks 
which  appear  to  be  the  most  extensively  developed. 

224.  The  period  of  time  represented  by  the  formation 
of  these  most  ancient  sedimentary  rocks,  and  by  the  un- 
stratified  or  igneous  rocks  below  them,  is  generally  termed 
the  Azoic  (wanting  in  vestiges  of  animated  nature),  inas- 
much as  we  have  little  or  no  evidence  that  any  form  of 
animal  or  vegetable  life  existed  at  that  epoch  upon  the 
surface  of  the  earth — all  the  rocks  above  described  being 
characteristically  barren  of  fossils.f 

225.  Scenery  of  the  Azoic  Period, — A  picture  of  the  scenery  of 
this  period  of  the  earth's  history  has  thus  been  imagined  by  Hugh  Miller. 
During  the  earlier  part  of  the  Azoic  period,  "wo  may  imagine,"  he  says,  "a 
dark  atmosphere  of  steam  and  vapor,  which  for  age  after  age,  conceals  the 
face  of  the  sun,  and  through  which  the  light  of  moon  or  stars  never  pene- 
trates; oceans  of  thermal  water,  heated  in  a  thousand  centers  to  the  boiling' 
point ;  low,  half-molten  islands,  dim  through  the  fog,  and  scarce  more  fixed 
than  the  waves  themselves  that  heave  and  tremble  under  the  impulsions  of 
the  igneous  agencies ;  roaring  geysers,  that  ever  and  anon  throw  up  their 
intermittent  jets  of  boiling  fluid,  vapor,  and  thick  steam,  from  these  tremulous 
lands ;  and  in  the  dim  outskirts  of  the  scene,  the  red  gleam  of  fire  shot  forth 
from  yawning  cracks  and  deep  chasms.  Such  would  be  the  probable  state  of 

things  among  the  times  of  the  earlier  gneiss  and  mica-schist  deposits — times 

•        ^___ 

QUESTIONS. — What  rocks  of  these  series  are  most  extensively  developed?    What  name 
is  given  to  the  period  represented  by  the  formation  of  the  oldest  rocks  ? 


*  The  physical  characters  and  mineral  composition  of  these  rocks  has  been  particularly 
described  in  Chapter  VI.,  entitled  "Varieties  and  Lithological  Characters  of  the  Meta- 
morphic  Rocks." 

t  The  student  should  here  be  cautioned  against  receiving  the  impression  that  gneiss, 
mica-schist,  talcose-schist,  hornblende-schist,  quartz  rock,  clay-slate,  etc.,  wherever  found, 
belong  exclusively  and  invariably  to  the  Azoic  period.  On  the  contrary,  rocks  possessing 
the  same  characters  are  occasionally  found  interstratified  with  fossiliferous  rocks  of  other 
and  much  more  recent  geological  periods.  All  the  rocks  above  enumerated  are  supposed 
to  be  sedimentary  rocks,  changed  and  altered ;  and  although  they  are  the  especially  char- 
acteristic rocks  of  the  Azoic  period,  yet  similar  formations  have  been  produced  wherever 
metamorphic  influences  have  operated  under  similar  circumstances. 


BOCKS     OF     THE     AZOIC      PERIOD.  205 

0 

buried  deep  in  that  chaotic  night  which  must  have  continued  to  exist  for, 
mayhap,  many  ages  after  that  beginning  of  things  in  which  God  created  the 
heavens  and  the  earth." 

"  At  length,  however,  as  the  earth's  surface  gradually  cooled  down,  and  the 
enveloping  waters  sunk  to  a  lower  temperature — let  us  suppose,  during  the 
latter  times  of  the  mica-schist  and  the  earlier  times  of  the  clay-slate— the 
steam  atmosphere  would  become  less  dense  and  thick,  and  finally  the  rays  of 
the  sun  would  struggle  through  it,  at  first  doubtfully  and  diffused,  forming  a 
faint  twilight,  but  gradually  strengthening  as  the  latter  ages  of  the  slato 
formation  passed  away,  until,  at  the  close  of  the  great  primary  period,  day 
and  night — the  one  still  dim  and  gray,  the  other  wrapped  in  a  pall  of  thickest 
darkness — would  succeed  each  other  as  now,  as  the  earth  revolved  on  its 
axis." 

226.  Fanciful  and  imaginative  as  this  picture  of  Hugh  Miller  undoubtedly 
is,  it  must  nevertheless  be  confessed  that  the  structure  of  the  rocks  of  the 
Azoic  period  does  not  militate  against  its  correctness.  Thus,  no  one  of  the 
rocks  to  which  a  sedimentary  origin  is  ascribed,  exhibits  more  remarkable 
examples  of  flexures  and  contortions  than''  the  older  or  fundamental  gneiss ; 
and  the  most  unskilled  observer,  on  inspecting  them,  is  irresistibly  led  to  the 
conclusion  that  the  layers  of  the  rock  were  once  in  a  semi-fluid  state,  and  in 
that  condition  were  subjected  to  great  disturbance.  (See  §  80,  also  Figs.  23, 
25,  and  27.)  "In  the  overlying  layers  of  mica,  talcose,  and  hornblende- 
s,chists,  there  is  also  much  contortion  and  disturbance ;  whereas  the  clay-slate, 
which  lies  at  the  top  of  the  series,  gives  evidence,  in  its  mere  mechanical 
texture  arid  the  regularity  of  its  strata,  that  a  gradual  refrigeration  had  been 
taking  place,  and  that  the  close  of  the  Azoic  period  was  comparatively  cool 
and  quiet." — MILLED. 

2-27.  Classification  of  the  Rocks  of  the  Azoic  Period.— 
We  have  already  said  that  geologists  are  not  fully  agreed  as  to  the  manner, 
in  which  the  stratified  rocks  of  the  Azoic  period — the  gneissic  rocks,  the 
schists,  clay-slates,  etc. — should  be  arranged  into  systems  or  groups.  The 
nomenclature  also  used  to  designate  them  by  different  authorities  is  not  uni- 
form. 

By  many  geologists,  especially  by  those  of  Great  Britain,  the  stratified 
rocks  here  referred  to  the  Azoic  period  have  been  divided  into  two  groups 
or  systems;— the  upper,  termed  the  "  Cambrian,"  from  Cambria,  ail  ancient 
name  of  North  "Wales,  where  the  system  is  extensively  developed;  while  the 
lower  and  older  rocks,  from  their  changed  and  altered  appearance,  have  been 
known  as,  or  called  the  "  Metamorphic  System." 

In  North  America,  the  stratified  rocks  of  the  Azoic  period  have  also  been 
divided,  by  the  geologists  engaged  in  conducting  the  survey  of  Canada,  into 
two  groups  or  systems — the  lower  system  being  designated  as  the  "  Lauren- 
tian,"  and  the  upper  as  the  "  Huronian" — names  derived  from  localities 

QUESTION.— In  what  manner  have  the  rocks  of  the  Azoic  period  been  classified  by 
different  geologists  ? 


206         FIRST      PRINCIPLES      OF      GEOLOGY. 

• 

where  the  rocks  in  question  have  been  especially  studied ;  namely,  the 
Laurentine  mountains  of  Canada,  and  a  district  in  the  vicinity  of  Lake 
Huron. 

The  eminent  American  geologists.  Profs.  "W.  B.  and  II.  D.  Rogers,  who 
have  conducted  the  geological  surveys  of  Virginia  and  Pennsylvania,  also 
divide  the  stratified  rocks,  formed  prior  to  the  Palaeozoic  period  (L  e.,  in  the 
Azoic  period),  into  two  groups,  but  designate  the  upper  group  as  the  Azoic, 
or  Semi-metamorphic ;  and  the  lower,  the  Hypozoic,  Gneissic,  or  True  Meta- 
morphic.  The  term  Hypozoic  (UTTO,  under ;  and  far],  life)  thus  used,  implies 
that  this  particular  class  of  rocks  is  not  only  barren  of  fossils,  but  that  it  lies 
below  all  the  formations  that  can  be  considered  as  fossiliferous. 

Taconic  System . — Another  distinguished  American  geologist  (Prof. 
E.  Emmons,  of  New  York)  considers  that  a  portion  of  the  older  sedimentary 
rocks  of  America  exhibit  such  marked  and  agreeing  characteristics  as  to 
warrant  their  arrangement  into  a  distinct  and  independent  system,  called  the 
Taconic ;  but  this  opinion  has  not,  however,  been  generally  accepted. 

The  enumeration  of  these  divisions  of  the  rocks  of  the  Azoic  period  may 
possibly  seem  to  the  student  as  needlessly  minute ;  but  as  they  are  constantly 
referred  to  in  modern  geological  treatises  and  discussions,  some  acquaintance 
with  them  is  certainly  desirable.  At  the  same  time,  the  classifications  of  the 
English  and  Canadian  geologists,  as  well  as  those  instituted  by  the  Messrs. 
Rogers,  may  be  considered  as  in  general  equivalent,  and  corresponding  to 
one  another.  With  these  explanations,  and  adopting  the  nomenclature  of. 
the  Canadian  geologists,  a  description  of  the  several  systems  will  now  be 
given  in  order. 


LAURENTIAN    SYSTEM. 
SYNONYMS. — Metamorphic  System — True  Metamorphic —  Gneissic — Ilypozoic. 

228.  The  Laurentian  mountains,  from  whence  this  sys- 
tem derives  its  name,  traverse  Canada,  north  of  the  St. 
Lawrence,  throughout  its  entire  length,  running  parallel 
with  the  river,  and  at  some  points  in  close  proximity  to 
it.  The  rocks  composing  this  system — principally  gneissic 
rocks,  crystalline  schists,  and  crystalline  limestones — are 
the  most  ancient  sedimentary  rocks  known  upon  the  con- 
tinent of  America  ;  and  are  supposed  to  correspond  in  age 
with  similar  ancient  rocks  found  in  Finland,  Scandinavia, 
and  the  north  of  Scotland. 

.  QUESTIONS. — What  relation  exists  between  its  differently  designated  divisions  ?  From 
whence  does  the  Laurentian  system  derive  its  name  ?  What  is  said  of  the  age  of  the 
Laursntian  rocks  ? 


LAURENTIAN     SYSTEM.  207 

Distribution, — In  North  America  the  Laurentian  system  extends 
throughout  Canada — including  the  Laurentian  mountains — and  through  a 
portion  of  the  Hudson's  Bay  Territory,  as  far  north  as  the  Arctic  Ocean. 
It  also  occupies  the  eastern  shores  of  the  continent,  north  of  the  Gulf  of  St. 
Lawrence.  In  New  York,  the  rocks  which  compose  the  Adirondac  Moun- 
tains are  believed  to  belong  to  this  system ;  as  do  also  the  rocks  which  con- 
stitute the  Ozark  Mountains  of  Missouri,  the  "Washita  Hills,  south  of  the 
Arkansas,  and  the  Whitchita  Mountains  of  Texas.  Another  area  of  these 
rocks  occurs  in  northern  Michigan. 

The  rocks  of  the  Laurentian  system  are  unfossiliferous,  or  azoic ;  and,  in 
fact,  are  generally  regarded  as  having  been  deposited  prior  to  the  introduc- 
tion of  life  upon  the  surface  of  our  planet.  They  are  everywhere  traversed 
by  veins,  or  immense  intrusive  masses  of  granite,  syenite,  porphyry,  or,  other 
eruptive  rocks — a  circumstance  which,  of  itself,  would  indicate  a  most  dis- 
turbed condition  of  the  crust  of  the  earth  during  the  period  of  their  formation. 

229.    Economic    Minerals    of    the    Laurentian    System, — 

The  rocks  of  the  Laurentian  system  afford  many  valuable  minerals.  Of  these 
the  most  important  are  ores  of  iron,  which  occur  for  the  most  part  associated 
with  hard,  crystalline  limestones.  In  Missouri,  the  deposits  of  iron  ore,  which 
exist  in  these  rocks,  are  among  the  largest  on  the  globe,  and  include  the  cele- 
brated Iron  Mountain,  which  is  300  feet  high,  two  miles  in  circumference,  and 
entirely  composed  of  magnetic  oxyd  of  iron.  Immense  deposits  of  iron  ore 
also  occur  in  Laurentian  rocks  in  the  Adirondac  district  of  New  York,  and 
at  various  localities  in  Canada.  Ores  of  lead,  copper,  and  baryta,  graphite 
(black-lead),  large  plates  of  mica,  and  many  valuable  gems,  are  also  afforded 
by  the  rocks  of  this  system  in  Canada  and  the  United  States. 

The  aggregate  thickness  of  the  rocks  of  the  Laurentian  system  in  North 
America  has  been  estimated  at  20,000  feet.* 

QUESTIONS.— What  of  their  distribution?  Do  they  afford  any  traces  of  fossils ?  What 
important  minerals  are  found  in  this  system?  "What  is  the  estimated  thickness  of  the 
Laurentian  rocks  of  North  America  ? 


*  Notwithstanding  what  has  heen  already  said  on  this  subject,  (see  §§  89,  96),  it  maybe 
a  matter  of  wonder  to  the  student  "  how  strata,  many  of  which  are  evidently  of  a  super- 
ficial nature,  can  be  collected  in  piles,  amounting  to  several  miles  in  thickness,  and  how 
such  an  extent  of  vertical  accumulations  can  ever  be  known  and  measured.  Coal  beds, 
for  example,  are  understood  to  have  been  deposited,  each  originally  at  the  surface,  yet 
they  are  repeated  at  intervals  of  variable  distances  apart,  amid  parallel  layers  of  sand- 
stones, shales,  and  limestones,  any  one  of  which  may  occupy  from  a  few  feet  to  one  hun- 
dred feet  or  more  in  its  recurrence.  Sandstones,  like  those  of  the  Connecticut  River 
Valley,  containing  impressions  of  tracks  of  animals,  are  also  found  in  beds  of  Several 
hundred  feet  in  thickness.  Now,  the  only  explanation  for  such  phenomena  must  be,  that 
the  surface  was  gradually  subsiding  during  the  periods  of  these  accumulations.  The 
times  of  slow  subsidence  were  represented  by  the  gathering  of  the  fine  sediments,  or  the 
growth  of  the  coal  plants,  and  those  of  rapid  subsidence  by  the  in-flow  of  the  coarse  sand 
and  pebbles  which  now  form  the  beds  of  sandstone  and  conglomerates.  Thus,  the  strata 
continued  to  be  piled  upon  each  other  so  long  as  the  same  system  of  operations  lasted  ? 
and  thus  it  was  that  the  Laurentian  rocks  reached  their  aggregate  thickness  of  20,000 


208          FIRST     PRINCIPLES     OF     GEOLOGY. 
CAMBRIAN,    OR    HURONIAN    SYSTEM. 

230.  In  many  localities  in  JSTorth  America  there  is 
found,  resting  unconformably  upon  the  rocks  .of  the  Lau- 
rentian  system,  a  series  of  schists,  slates,  hard  sandstones, 
and  conglomerates  (with  some  limestones);  which,  from 
the  fact  of  their  attaining  a  vertical  thickness  of  about 
12,000  feet  on  the  north  shore  of  Lake  Huron,  have  been 
termed  the  "  Huronian  System." 

The  constituents  of  these  rocks,  moreover,  have  evidently  been  mainly  de- 
rived from  the  waste  of  the  older  rocks,  on  the  eroded  surfaces  of  which  they 
rest.  They  also  exhibit  less  striking  evidence  of  metamorphic  action  than 
the  rocks  of  the  Laurentian  system  beneath  them. 

In  Europe,  a  series  of  rocks,  supposed  to  correspond  with  the  Huronian  in 
geological  age  and  position,  is  known  as  the  Cambrian,  and  is  very  extens- 
ively developed  in  Great  Britain,  Bohemia,  and  Scandinavia — the  beds  in 
some  localities  attaining  an  apparent  thickness  of  26,000  feet.  In  Great 
Britain  especially,  the  Cambrian  system  includes  vast  beds  of  clay-slate,  which 
in  Wales  furnish  the  celebrated  quarries  of  "Welsh  roofing  slate. 

•FIG.  113.  231.  Notwithstanding  the  great  thickness  of 
the  rocks  of  this  system,  they  afford  scarcely 
any  traces  of  the  existence  of  life  during  the 
period  of  their  deposition. 

In  America  and  Bohemia  none  whatever  have  been  re« 
cognized;  but  in  Great  Britain,  in  the  clay-slates,  which  occur 
high  up  in  the  system,  and  appear  to  have  been  deposited 
as  fine  sediments  in  quiet  waters,  a  few  fossils  have  been  dis- 
covered. The  principal  of  these  are  the  impressions  of  a 
small,  plant-like  zoophyte,  Fig.  11*3  (called  Oldhalmia,  from 
Prof.  Oldham,  its  discoverer),  a  few  fucoids  (sea- weeds),  and  certain  tracks 
and  burrows,  which  are  believed  to  have  been  made  by  marine  worms. 

QUESTIONS. — What  rocks  are  super-imposed  upon  the  Laurentian  System  in  this  coun- 
try ?  What  is  said  of  their  composition  and  character  ?  What  corresponding  series  of 
rocks  exists  in  Europe  ?  What  organic  remains  have  been  afforded  by  this  system  ? 

feet.  When  uplifted  to  form  the  hills  and  valleys  of  a  continent,  their  horizontal  ar- 
raTIgement  is  disturbed,  the  strata  are  turned  upward  so  as  to  present  disrupted  ends  and 
edges  (see  Figs.  31  and  42),  and  by  their  sloping  and  undulating  position,  each  in  its  turn 
is  brought  to  the  surface,  and  all  may  be  measured,  some  in  one  locality  and  some  iq 
another.  Subsequently  to  this  uplifting,  denuding  forces  have  been  in  action,  removing 
immense  portions,  chiefly  of  the  most  elevated  masses,  and  building  up,  in  more  recent 
seas,  newer  formations  from  the  wreck  of  the  old,  in  the  same  manner  as  these  had  been 
produced.  Thus,  after  a  systematic  plan,  and  with  evident  provision  for  the  future 
wants  of  man,  the  various  useful  materials  of  all  tho  strata  are  brought  within  his  reach." 


CAMBRIAN,    OB     HURONIAN     SYSTEM.      209 

The  interest  which  attaches  to  these  few  fossils  is  very  great ;  for  as  the 
most  assiduous  researches  have  thus  far  failed  to  detect  any  other  traces  of 
organization  in  this  system,  we  may  fairly  regard  these  relics  as  the  repre- 
sentatives of  the  first  forms  of  life  that  appeared  upon  our  planet.  Had  other 
animals  or  plants  really  existed  during  this  ancient  epoch,  it  seems  probable 
that  some  indications  of  them  would  have  been  discovered ;  especially  as  the 
hardened  sediments,  in  which  the  above-mentioned  fossils  occur,  are  com- 
posed of  such  fine  particles,  and  are  so  little  altered,  that  they  have  retained 
the  most  minute  impressions  which  have  been  made  upon  their  surfaces. 

Thus,  in  some  instances,  where  the  strata  appear  to  have  constituted  the 
shore  of  an  ancient  ocean,  they  are  covered  with  distinct  wave  or  ripple- 
markings;,  in  others,  "they  have  evidently  been  subjected  to  a  drying  pro- 
cess, so  that,  as  happens  with  the  bottom  of  a  muddy  pool,  laid  dry  during  a 
summer  drought,  they  are  cracked  into  irregular  polygonal  divisions;  and  as, 
when  again  submerged,  a  sudden  deposition  filled  up  the  cracks,  we  can  still 
trace  the  marks  of  desiccation  as  distinctly  in  the  stone  as  if  they  had  been 
made  by  the  sun  of  a  previous  week." 

FIG.  114 


Tho  same  surfaces  are  also  frequently  covered  with  small  pits  or  impres- 
sions, which  are  believed  to  have  been  made  by  the  striking  of  drops,  of  rain; 
and  these,  sometimes,  by  their  uniform  obliquity  of  imprint,  clearly  register 
the  direction  in  which  the  wind  was  blowing  at  the  time  of  their  production. 
Fig.  114  represents  the  upper  and  under  surface  of  a  thin  layer  of  shalo 
marked  with  rain  impressions  and  worm-tracks. 

Such  impressions  or  markings,  are  not,  however,  confined  to  the  rocks  of 
the  Cambrian  system;  but,  on  the  contrary,  they  may  be  observed  upon 
almost  all  strata,  composed  of  finely  divided  particles,  which  have  been  de- 
posited under  similar  circumstances. 

QUESTIONS. — What  peculiar  interest  attaches  to  them?  What  interesting  markings 
characterize  some  of  the  rocks  of  this  system,? 


210       FIRST     PRINCIPLES     OF     GEOLOGY. 


PALEOZOIC  PERIOD. 

232.  The  stratified  rocks  of  the   Palaeozoic  period  are 
arranged  into  four  systems,  viz. :  the  Silurian,  the  Dev- 
onian, the  Carboniferous,  and  the  Permian. 

SILURIAN    SYSTEM. 

233.  This  system  of  stratified  rocks  derives  its  name 
from  the  circumstance  that  it  was  first  studied  and  in- 
vestigated3  by  Sir  E.  I.  Murehison,  in  the  district  of  coun- 
try between  England  and  Wales,  anciently  inhabited  by  a 
tribe  of  the  Britons,  called  "  Silures." 

Distribution , — The  existence  of  this  system,  in  Great  Britain,  was  de- 
termined by  Sir  R.  I.  Murehison,  in  1839.  Since  then,  an  equivalent  series 
of  rocks  has  been  ascertained  to  exist  in  most  of  the  countries  of  the  globe. 
Thus,  they  have  been  found  in  Great  Britain,  Scandinavia,  Germany,  Russia, 
France,  Spain,  Portugal,  Turkey,  various  parts  of  Eastern  Asia,  through- 
out Siberia,  in  South  Africa,  Australia,  and  even  at  the  Falkland  Islands,  in 
the  extreme  southern  hemisphere. 

In  North  America,  a  series  of  rocks,  of  the  same  age  and  geological  posi- 
tion, is  developed  upon  a  most  gigantic  scale,  covering  a  vast  extent  of, 
Canada  and  the  Hudson's  Bay  Territory,  and  occupying,  in  detached  masses, 
an  area  in  the  United  States  more  than  a  thousand  miles  in  length — from 
Canada  to  Alabama — and  extending  from  New  York,  westward  through  the 
Yalley  of  the  Ohio,  to  points  beyond  the  Mississippi. 

In  ah1  these  districts,  so  geographically  remote,  the  system  is  marked  by 
the  same  peculiar  fossils ;  and  though  the  strata  may  differ  very  greatly  as 
regards  their  mineralogical  composition — shales  in  one  locality  being  replaced 
by  slates  in  another,  sandstones  by  quartz  rocks,  and  soft  calcareous  rocks 
by  hard  limestones — yet  the  moment  the  geologist  detects  certain  character- 
istic organic  remains  he  can  have  no  doubt  as  to  their  position  in  the  geologi- 
cal series. 

234.  Characteristics  of  the    Silurian    System. — Under  what- 
ever circumstances  the  strata,  which  constitute  the  systems  (Laurentian  and 
Huronian)  which  precede  the  Silurian,  were  deposited,  they  exhibit,  for  the 
most  part,  as  has  been  already  stated,  a  peculiar  metamorphic,  or  altered 
appearance ;  while  the  lines,  which  indicate  the  alternations  of  deposits  of 

QUESTIONS. — What  systems  are  included  in  the  Palaeozoic  period  ?  What  is  the  deriva- 
tion of  the  name  Silurian?  What  is  said  of  the  distribution  of  the  rocks  of  this  system  ? 
Are  the  strata  of  the  Silurian  system  all  alike,  mineralogically,  in  different  parts  of  the 
world  ? 


SILURIAN      SYSTEM. 


211 


sedimentary  matter,  are  indistinct,  and  often  entirely  obliterated.  "We  can 
not,  for  example,  in  inspecting  a  formation  of  gneiss,  mica-schist,  hornblende- 
schist,  quartz-rock,  or  other  crystalline  sedimentary  deposit,  say  exactly  what 
was  the  original  condition  of  its  constituent  particles ;  neither  can  we  arrive 
at  any  satisfactory  conclusions  as  to  the  nature  of  the  seas  in  which  they 
were  deposited. 

In  the  Silurian  system,  however,  the  aspect  of  a  series  of  strata  is  wide]y 
different.  Every  alternation  of  deposit  is  distinct  and  evident.  Beds  of 
shale,  sandstones,  pebbly  conglomerates,  argillaceous  slates  and  limestones, 
follow  one  another  in  frequent  succession,  and  retain  their  original  structure 
so  perfectly,  that  it  is  not  difficult  to  judge  of  the  circumstances  of  their  for- 
mation. 

FIG.  115. 


The  Silurian  system  in  Europe  rests  upon  the  rocks  of 
the  Cambrian  system.  In  this  country  it  rests  uncon- 
formably  upon  the  Huronian  rocks,  in  the  vicinity  of  Lake 
Huron,  *  and  elsewhere  (in  localities  where  the  Huronian 
rocks  are  wanting),  upon  the  Lauren tian  system. 

Fig.  115  represents  the  manner  in  which  the  rocks  of  the  Silurian  sys- 
tem rest  unconformably  upon  gneiss,  at  the  Falls  of  Montmorency,  Canada 
East. 

235.  Divisions  of  the  Silurian  System, — The  rocks  of 
the  Silurian  system  may  be  divided  into  three  great 
groups,  viz.  :  the  UPPER,  MIDDLE,  and  LOWER  SILU- 


QTTESTIONS. — How  are  they  recognized  ?  As  compared  with  the  formations  of  the  pre- 
ceding1 systems,  what  are  the  characteristics  of  Silurian  rocks  ?  Upon  what  basis  does 
this  system  rest  ? 


*  The  attention  of  the  student  is  here  particularly  directed  to  the  great  significance 
of  the  circumstance  of  an  unconformahility  (see  §  94)  between  the  stratified  rocks  of 
two  systems  or  series.  In  this  particular  instance,  it  implies  unmistakably  that  the 
rocks  of  the  Huronian  system  were  deposited,  consolidated,  and  elevated  into  angular 
positions,  before  the  epoch  of  the  formation  of  the  Silurian  system  commenced— a  series 
of  events  which  must  have  required  a  vast  period  of  time  (the  Huronian  system  being 
12,000  feet  thick),  as  well  as  the  action  of  powerful  disturbing  forces. 


212      FIRST     PRINCIPLES     OF     GEOLOGY. 

RIAN;  which  are  distinguishable  from  each  other  hy  a 
want  of  conformity,  or  by  the  peculiarities  of  their  con- 
tained fossils. 

236.  Subdivisions  , — These  three  groups  in  America  have  been  further 
subdivided  into  (at  least)  fourteen  minor  groups,  or  series  of  Strata,  which 
have  been  named  mainly  from  localities  in  the  State  of  New  York,  where  the 
rocks  in  question  are  typically  developed.  They  are  as  follows,  commencing 
with  the  lowest : 

LOWER     SILURIAN. 

1.  Potsdam  Sandstone. 

2.  Chazy  Limestone. 

3.  Caldferous  Sand-rock.    ~| 

4.  BirXs-eye  Limestone.      I  Trenton  G 

6.  Slack  River  Limestone.  [ 
G.  Trenton  Limestone.         J 

7.  Utica  Slates  )  Hudson  River  Group,  or  the 

8.  Hudson  River  Slates.  J  Blue,  or  Galena  Limestone  of  the  West. 

MIDDLE     SILURIAN. 

9.  Oneida  Conglomerate,  or  Sillenj  Sandstones  of  Canada. 
10.  Medina  Sandstone. 

10.  Clinton  Group. 


UPPER     SILURIAN, 

11.  Niagara  Shale.         7  _ 

12.  Niagara  Limestone.?  Ma-ara  GrouP' 

13.  Onondaga  Salt  Group. 

14.  Lower  Helderberg  Group. 

FlG.  116. 


WESTERN  NEW  YORK,, 


UPPER.  CANADA 


QUESTIONS.— How  are  the  rocks  of  the  Silurian  system  divided?    What  is  said  of  the 
subdivisions  of  the  principal  groups? 


SILURIAN      SYSTEM 


213 


Fig.  116  shows  the  position  of  the  rocks  of  the  Silurian  system  as  they 
occur  in  Upper  Canada  and  Western  New  York.  On  the  left,  it  will  be  ob- 
served that  they  rest  upon  the  Laurentian  system,  and  are  succeeded  upon 
the  right  by  the  rocks  of  the  Devenian  system.  In  this  section  the  Huronian 
rocks  are  wanting,  as  well  as  are  several  of  the  other  subdivisions ;  it  being 
very  rare  to  find  all  the  divisions  of  a  system  in  one  locality. 

In  Europe,  similar,  or  equivalent  divisions  of  the  rocks  of  the  Silurian  sys- 
tem, have  been  recognized,  but  the  names  by  which  they  are  designated  are 
different  from  those  adopted  in  America. 

237.  Life  of  the  Period  Represented  by  the  Silurian 
System, — In  the  rocks  deposited  during  the  period  of  the 

FIG.  117. 


earth's  history,  represented  hy  the  Silurian  system,  the 
remains  of  animals  are  often  exceedingly  abundant.  They 
are,  however,  almost  exclusively  the  remains  of  inverte- 

QUESTION.— Have  equivalent  divisions  been  recognized  in  Europe  ? 


214        FIRST     PRINCIPLES     OF     GEOLOGY. 

brate*  marine  animals — i.  e.,  corals,  echinoderms,  molluscs, 
annelids  (worms),  and  Crustacea— a  circumstance  which 
induces  the  belief  that  only  a  small  portion  of  what  is  now 
dry  land  was  then  above  the  surface  of  the  water. 

Fig.  117  is  a  map,  showing  (approximately)  how  much  of  the  present 
continent  of  Europe  was  elevated  above  the  water  during  the  Silurian  epoch  ; 
the  unshaded  portions  representing  land. 

238.  Lower   Silurian , — In  the  lower  Silurian  rocks,  no  trace  of  a  fish, 
or  of  any  of  the  higher  manifestations  of  vertebrate  existence,  has  ever  been 
detected ;  and  although  we  find  in  them  delicately  rippled-marked  shales  and 
sandstones,  which  point  to  the  existence  of  quiet  wave- washed  shores ;  and 
pebbly  conglomerates,  which  bespeak  gravel  beaches,  yet  not  a  trace  of  a 
land  plant,  any  more  than  of  a  fish,  can  be  discovered.     "It  seems  to  have 
been,"  says  Hugh  Miller,  "for  many  ages  together,  a  creation  of  molluscs, 
corals,  and  Crustacea." 

239.  The  first  positive  evidence  of  the  existence  of  life  in  the  American 
series  of  stratified  rocks  occurs  in  the  Potsdam  sandstone,  which  constitutes 

FIG  118  *ke  base  of  the  Lower  Silurian  group. 

In  this  formation,  the  greatest  thick- 
ness of  which  is  about  300  feet,  a  very 
few  species  of  fossils  have  been  found. 
Of  these,  the  most  characteristic  is 
a  small  bivalve  shell,  called  Lingula^ 
(see  Fig.  118),  which  also  occurs  in 
that  division  of  the  Lower  Silurian 
rocks  of  Europe  which  is  supposed  to 
be  equivalent  in  age  and  position  to 
the  Potsdam  sandstone  of  America. 

There  are  also  found  in  these  oldest 
Silurian  strata,  the  remains  of  an  exceedingly  curious  family  of  Articulate  (joint- 
ed) animals,  which,  from  the  circumstance  that  their  shell  or  body  is  divided 
into  three  lobes  or  parts,  are  called  TriloUtes.  (Gr.,  rpcif,  three  ;  and  /.o/3of,  a 
lobe.)  See  Figs.  119,  120,  and  121.  When  first  discovered,  these  fossils  were 
supposed  to  be  the  remains  of  insects,  but  they  are  now  known  to  belong  to 
the  class  Crustacea.  The  animals  were  of  oval  figure,  protected  by  a  shell 
which  covered  the  anterior  part  of  the  body,  while  the  abdomen,  or  posterior 

QUESTIONS.— What  is  said  of  the  life  of  the  period  represented  by  the  Silurian  system  ? 
What  is  the  character  of  the  fossils  of  the  Lower  Silurian  ?  In  what  member  of  the 
Silurian  system  in  America  do  we  find  the  first  traces  of  life?  What  are  some  of  the 
principal  fossils  found  in  the  Potsdam  sandstone? 


*  Invertebrate— without  vertebrae  or  a  back-bone— usod  ia  contradistinction  to  verte- 
brate. 


SILURIAN      SYSTEM. 


215 


portion,  had  numerous  segments,  that  folded  over  each  other  like  the  plates 

in  a  lobster's  tail.    By  this  arrangement  they  were  enabled  to  roll  themselves 

up  into  a  ball,  so  as  to  present  their  hard  plates  in  all  directions  in  self-de- 

FiG.  119:  FiG.  120.  FlG.  121. 


FIG.  122. 


fense;  as  do  the  wood-louse  and  the  armadillo  of  the  present  day.  In  this 
condition  they  are  often  found.  Their  eyes,  which  in  many  specimens  are 
very  perfectly  preserved,  were  very  curious,  and  consisted  of  a  great  number 
of  angular  facettes,  or  lenses,  similar  to  the  eye  of  the  dra- 
gon fly  (in  which  there  are  25,000).  "In  order  to  ex- 
tend the  field  of  vision,  since  the  eye  was  immovable,  it 
was  elevated  above  the  body;  while  its  form  was  that  of 
the  .frustrum  of  a  cone,  incomplete  on  the  side  opposite 
the  corresponding  part  of  the  other  eye ;  thus  enabling 
the  animal  to  see  in  all  directions  horizontally."  This 
structure  of  the  eye  indicates  that  the  phenomena  of  light, 
and  the  conditions  of  vision,  were  essentially  the  same 
during  the  Silurian  epoch  as  at  the  present  time;  and 
also,  that  the  trilobites  lived  in  water  sufficiently  trans- 
parent to  transmit  light.  It  may  be  also  remarked,  in  this  j 
connection,  that  Hugh  Miller  has  suggested,  that  the  ex-  ' 
istence  of  a  clear,  transparent  atmosphere  was  the  most  "' 
conspicuous  feature  which  distinguished  the  scenery  of 
the  Silurian  epoch  from  that  of  the  close  of  the  Azoic 
period. 

Fig.  122  represents  one  of  the  eyes  of  the  Trilobite 
(magnified),  as  it  is  found  fossil. 

The  Trilobites  were  among  the  most  abundant  of  the  early  forms  of  life 
that  peopled  our  globe — no  less  than  400  distinct  species  having  been  recog- 


.— Describe  the  Trilobites.     What  is  said  of  their  abundance  ? 


216       FIRST     PRINCIPLES     OF     GEOLOGY. 


nized  in  the  Paleeozoic  systems.  They  varied  in  length  from  one  to  twenty 
inches;  and  seemed  to  have  swarmed  in  the  Silurian  waters,  just  as  crabs 
and  shrimps  swarm  in  the  seas  of  our  day — whole  rocks,  in  some  instances, 
being  formed  almost  exclusively  of  their  remains.  In  the  Trenton  limestone, 
at  Trenton  Falls,  N.  Y.,  they  may  be  seen  in  the  greatest  profusion. 

As  a  race,  the  Trilobites  continued  to  flourish  (i.  e.,  different  species)  during 
the  whole  of  the  Silurian  epoch,  but  gradually  died  out  in  the  epoch  of  the 
Devonian  system,  and  entirely  disappeared  from  creation  in  the  Carboniferous 
system,  since  when,  no  representative  of  these  curious  animals  has  existed. 

FIG.  123.  FIG.  124. 


240.  As  we  ascend  in  the  series  of  the  Lower  Silurian  rocks,  the  forms  of 
life  are  found  to  multiply  rapidly ;  and  in  the  groups  of  strata  immediately 
succeeding  the  Potsdam  sandstone,  which,  as  already  stated,  contains  but  a 
few  species,  the  fossil  remains  of  more  than  one  hundred  distinct  species  of 
invertebrate  animals  .have  been  discovered. 

Some  of  the  most  common  forms  in  these  ancient  sedimentary  deposits  be- 
long to  a  family  of  plant-like  zoophites  (radiata),  known  to  geologists  by  the 
general  name  of  Graptolites.  They  seem  to  have  lived  upon  a  muddy  bottom 
and  to  have  thrown  out,  in  all  directions,  from  a  center,  (see  Fig.  123)  small 
serrated  or  feather-like  arms.  Fig.  124  represents  portions  of  the  arms  of 
graptolites. 

The  remains  of  corals  are  also  found  in  the  greatest  abundance;  more 
species  occurring  in  the  different  divisions  of  the  Silurian  rocks  in  the  State 

QUESTIONS. — In  what  locality  in  the  United  States  are  their  remains  particularly  notice- 
able ?  What  is  observed  as  we  ascend  in  the  series  of  Lower  Silurian  rocks  ?  What 
are  some  of  the  most  common  forms  of  life  in  these  deposits  ? 


SILURIAN      SYSTE 


217 


of  New  York  alone,  than  are  now  living  upon  the  coast  of  Florida.  Fig.  95 
represents  various  forms  of  Silurian  corals;  Fig.  125,  a  species  (Columnaria 
alveolata)  from  the  Black  River  limestone  of  N.  Y. ;  and  Fig.  126.  a  beauti- 
ful species  of  chain  coral,  which  is  peculiar  to  the  Upper  Silurian. 

FIG.  126. 


Besides  graptolites  and  corals,  the  radiata  are  represented  in  both  the 
Upper  and  Lower  Silurian  rocks  by  a  curious  and  beautifully  organized 
family  of  Echinoderms,  which,  from  the  resemblance  of  some  species  to  a 
lily,  have  been  called  Crinoids  (Gr.,  Kpivor,  lily;  and  eidof,  form),  and  also 
Encrinites.  As  these  animals  were  developed  more  fully  at  a  later  geologi- 
cal epoch,  we  defer  further  notice  of  them  until  we  come  to  the  Carboniferous 
system,  but  for  the  present  a  good  idea  of  their  form  may  be  obtained  by  e£- 
amining  Figs.  29  and  111. 


FiG.  128. 


FIG.  129. 


Great  numbers  of  molluscs  (shells)  are  also  found  in  all  the  groups  of  the 
Silurian  system,  and  comprise  representatives  of  each  of  the  three  cl 
viz.:  Acephala,  Gasteropoda,   and  Cephalopoda  (see  §  198);    some 
being  closely  allied  to  existing  forms,  while  others  have  no  likeness  to  any 

10 


218       FIRST     PRINCIPLES     OF     GEOLOGY. 


130. 


living  animal.  Figs.  127,  128,  and  129  represent  some  of  the  most  common 
of  these  fossils — Fig.  127  representing  a  bivalve  shell,  termed  Terebratula  ; 
Fig.  128,  a  similar  shell,  known  by  the  name  of  Oriliis;  and  Fig.  129,  a 
gasteropod,  univalve  shell,  called  Bdlerophon. 

Many  of  the  Silurian  shells  are  chambered 
(Cephalopoda);  some  being  curved  or  coiled  as 
in  the  species  termed  Lituites  (Fig.  130);  while 
others  are  straight.  Of  these  last,  the  most  in- 
teresting are  the  so-called  Orthoceratites  (Gr., 
op$of,  straight ;  and  itepa^,  a  horn).  They  con- 
sisted of  a  straight  shell  (see  Fig.  131),  divided 
into  numerous  chambers  by  septa  or  partitions, 
which,  in  turn,  wero  perforated,  so  that  a  tube 
(siphuncle)  might  communicate  with  all  of  them.  They  are  found  of  all 
sizes,  from  a  few  inches  to  ten  feet  in  length,  and  a  foot  in  diameter.  In 
some  specimens  upward  of  seventy  chambers  have  been  counted.  In  many 
of  the  Silurian  rocks  (Black  River  Limestone,  and  Trenton  Limestone,  N.  Y.) 
they  occur  so  abundantly  as  to  overlie  and  touch  each  other,  rendering  it 
difficult  to  procure  a  perfect  specimen.  This  family  continued  to  be  repre- 
sented by  different  species,  in  the  Devonian,  Carboniferous,  and  Triassic  sys- 


tems, when  it  became  extinct.  Fig.  131,  a,  shows  a  part  of  the  shell  of  an 
Orthoceratite ;  l>,  a  vertical  section  of  the  shell,  showing  the  chambers  and 
the  central  tube  running  through  them;  c,  one  of  the  septa  or  partitions ; 
and  d,  the  termination  of  the  shell,  with  the  outer  shell  partially  removed. 

With  regard  to  the  vegetation  that  flourished  upon  the  earth  during  the 
the  Lower  Silurian  epoch,  we  have  no  very  satisfactory  evidence ;  and  thus 
far,  the  only  remains  discovered,  appear  to  have  belonged  to  low  orders  of 
marine  plants  or  sea-weeds.  These  occur,  however,  very  abundantly  in 

QUESTIONS. — What  was  the  character  of  the  vegetation  of  'jhe  Lower  Silurian  ? 


SILURIAN      SYSTEM.  219 

some  localities,  and  in  the  Lower  Silurian  rocks  of  England  they  even 
compose  impure  beds  of  anthracite  coal  several  feet  in  thickness.  In 
all  cases  the  individual  plants,  apparently  from  the  original  looseness  of 
their  texture,  are  but  indifferently  preserved,  so  that  it  is  difficult  to  trace 
any  very  close  resemblance  be- 
'tween  them  and  the  plants 
which  darken  the  half-tide 
locks  of  our  coasts  at  the 
present  time.  Fig.  132  repre- 
sents the  appearance  of  one 
of  the  oldest  of  these  fossil  sea- 
weeds from  the  Lower  Silurian 
of  America — the  Phytopsis  tubu- 
losum  of  the  Bird's-eye  Lime- 
stone of  New  York.  .- 

241.  Middle  and  Upper  Silurian , — The  question  may  here  natu- 
rally suggest  itself  to  the  learner ;  What  reasons  have  geologists  for  dividing 
tho  rocks  of  the  Silurian  system  into  two  or  more  groups — upper  and  lower — 
or  upper,  middle,  and  lower  ?  and  is  there  any  evidence  of  such  divisions 
really  existing  in  nature  ?  To  this  wo  reply,  that  in  many  localities  tho 
strata  of  the  Upper  and  Middle  Silurian  rests  unconformably  upon  those  of  tho 
Lower  Silurian ;  thus  showing  that  tho  Lower  Silurian  epoch  terminated  with 
a  more  or  less  general  disturbance  of  the  earth's  surface,  which  not  only  pro- 
duced a  break  in  tho  deposition  of  the  series  of  strata,  but  elevated  the  pre- 
viously formed  rocks  into  angular,  unnatural  positions.  AYo  also  find,  that 
between  these  two  epochs,  the  character  of  the  life  peopling  the  surface  of 
the  earth  manifestly  changed;  not  only  many  species,  but  even  some  entire 
genera  dying  out,  and  other  new  ones  being  introduced.  Thus,  according  to 
Prof.  Owen,  of  forty-three  genera  of  Trilobites,  found  in  the  Lower  Silurian 
rocks,  thirteen  genera,  including  many  species,  seem  to  have  entirely  perished 
before  the  Upper  Silurian  epoch  commenced,  while  other  species,  forming 
new  genera,  appear  for  the  first  time,  in  the  upper  group,  to  occupy  their 
places.  In  short,  while  the  fossils  found  in  tho  Middle  and  Upper  Silurian 
rocks  belong  to  the  same  classes,  the  same  orders,  and  in  many  instances  to 
the  same  genera  of  animals,  as  those  occurring  in  the  Lower  Silurian,  only  a 
comparatively  few  species  extend  over  the  break  (if  we  may  so  express  it), 
and  are  common  to  both  the  upper  and  the  lower  groups.  "  Thoee  long- 
surviving  species,"  says  a  recent  authority,  "  appear  to  have  lived  in  great 
depths  of  water,  and  to  have  ranged  over  large  areas  of  tho  earth's  surface," 
a  circumstance  which  may  account  for  their  exemption  from  tho  destruction 
that  involved  their  cotemporaries. 

The  species  of  marine  animals  (invertebrates)  are  more  numerous  in  the 
rocks  of  the  Middlo  and  Upper  Silurian  groups  than  in  those  of  the  Lower 
Silurian;  but  some  great  beds  of  limestone,  in  both  group?,  however,  can 

QUESTIONS.—  What  reasons  ifave  induced  geologists  to  divide  the  Silurian  system  into 
groups?  Are  the  same  fossils  found  in  all  the  divisions  of  the  Silurian  rocks? 


220       FinST     PRINCIPLES     OF     GEOLOGY. 


FIG.  133. 


scarcely  be  regarded  as  deposits  at  all,  inasmuch  as  every  calcareous  particle 
of  which  they  are  composed,  was  at  one  time  associated  with  animal  life,  as 
the  segments  of  Trilobites,  the  frame- work  of  corals,  or  the  shells  of  molluscs; 
all  of  which  lived  and  died  upon  the  spot  that  the  rocks  now  occupy. 

Of  the  corals  of  the  Upper  Silurian, 
Fig.  133  represents  one  of  the  most  strik- 
ing species — Cyathophyllum — the  re- 
mains of  which  are  often  mistaken  for 
fossil  horns.  Fig.  134  represents  a  curi- 
ous cup-shaped  coral,  the  Cyathaxonia. 
Concerning  these  ancient  corals,  a 
very  curious  fact  has  been  noticed, 
which  the  student  can  verify  for  him- 
self; namely,  they  are  all  stars  of  four 
rays,  or  of  multiples  of  four ;  while  the 

FIG.  134 


modern  corals  are  stars  of  six  rays,  or  of  multiples  of  six.  At  a  certain  de- 
finite epoch,  however  (about  the  close  of  the  Palaeozoic  period),  nature,  iu 
forming  this  class  of  creatures,  discarded  the  .number  four,  and  adopted 
the  number  six ;  retaining  at  the  same  time  the  idea  of  the  star  pattern,  which 
characterizes  equally  the  modern  and  the  ancient  types. — HUGH  MILLER. 

Figs.  135,  136,  137,  and  138  represent  a  few  of  the  characteristic  shells 
of  the  Upper  Silurian:  Fig.  135,  Leptosna  depressa ;  Fig.  13G,  Delthyris  Niagar- 
ensis;  Fig.  137,  Spirifer  radiatus;  and  Fig.  138,  a  fossil  shell  termed  Penta- 
merus,  some  species  of  which  occur  in  such  abundance  that  they  form  no  incon- 
siderable part  of  the  mass  of  some  limestones  belonging  to  the  Helderberg 
series  of  the  (American)  Upper  Silurian  group — viz.,  the  Pentamerus  limestones. 

New  forms  of  Crustacea  make  their  appearance  at  tho  close  of  the  system, 
some  of  which  resembled  our  present  lobsters  in  external  shape,  but  appear 
to  have  had  a  length  of  from  six  to  eight  feet— a  circumstance  which  strik- 
ingly illustrates  a  characteristic  of  the  animals  and  plants  of  these  ancient 
times — namely,  that  they  united  great  size  with  such  u  low  grade  of  organi- 
zation, as  at  the  present  day  we  find  to  be  always  restricted  to  forms  com- 
paratively minute.  • 

QUESTIONS.— What  is  said  of  tlio  abundance  of  animal  remains  iu  the  Upper  Silurian 
rocks?  What  new  forms  of  fossils  occur  in  the  uppermost  rocks  of  the  Silurian  system  ? 


SILURIAN      SYSTEM. 
FIG.  135. 


221 


FIG.  136. 


FIG.  139. 


Of  marine  plants,  or  sea- weeds,  ten  species  havejjeen  described,  from  the 
Upper  Silurian  rocks  of  America,  one  of  the  most  interesting  of  which  (Arthro- 
phycus  Harlani)  is  represented  by  Fig.  139. 

Fig.  107  represents  a  fossil  Silurian  star-fish;  and  Fig.  140,  certain. tracks 
or  markings  found  on  strata  of  the  Upper  Silurian,  which  are  supposed  to 
have  been  made  by  marine  worms  (Annelids),  crawling  over  a  mud  surface. 

242.  Fishes, — In  the  uppermost 
rocks  of  the  Silurian  system,  immedi- 
ately under  the  base  of  the  next  overly- 
ing system  (the  Devonian),  the  remains 
of  the  earliest  known  fishes  occur — as- 
sociated with  what  also  appears  for  the 
first  time,  namely,  the  fragmentary  re- 
mains of  a  terrestrial  vegetation — thus 
indicating  that  the  first  vertebrate  ani- 
mals, and  the  first  land  plants,  were 


FIG.  140. 


•%>„><*.  Vi\*J 

.f*S3»A«iH&*.v» 


called  into  existence  upon  our  planet  at  nearly  the  same  epoch.     As  these 
remains,  however,  seem  to  be  in  anticipation,  as  it  were,  of  a  greater  develop- 


222        FIRST     PRINCIPLES     OF     GEOLOGY. 

ment  of  the  same  forms  of  life  during  the  Devonian  era,  a  description  of  them 
is  deferred  for  the  present.* 

243.  The  Thickness  of  the   Silurian   System, — The  estimated 
aggregate  thickness  of  the  stratified  rocks  of  the  Silurian  system  varies  for 
different  countries.    In  North  America  it  has  been  estimated  at  about  11,500 
feet;  but  in  Great  Britain  the  estimates  are  much  greater,  viz.,  20,000  feet 
at  least  for  the  lower  Silurian  group,  and  7, GOO  for  the  middle  and  upper 
groups ;  or  an  aggregate  of  nearly  five  miles  of  strata.     Many  of  these  strata 
must,  moreover,  have  been  of  exceedingly  slow  deposition;  some  evidently 
having  been  deposited  at  the  bottom  of  profound  seas,  far  from  land,  and 
below  the  zones  of  animal  and  vegetable  life ;  while  others  were  undoubtedly 
formed  more  rapidly  in  shallow  tropical  seas,  swarming  with  marine  life.     It 
should  be  also  borne  in  mind,  that,  throughout  all  this  great  thickness  of 
strata,  no  remains,  or  trace  of  any  reptile,  bird,  or  mammal,  have  ever  been 
discovered ;  a  circumstance  which  may  be  considered  as  conclusive,  that  there 
were  none  of  these  animals  in  existence  at  this  epoch. 

244.  Mineral    Deposits  , — In  an  industrial  point  of  view,  the  rocks  of 
the  Silurian  system  are  of  no  great  importance.     Some  marbles  are  obtained 
from  the  series,  as  well  as  flagging  and  roofing  slates ;    also  some  archi- 
tectural sandstones,  and  limestones  suitable  for  building  and  mortar.     The 
mineral  deposits  belonging  to  the  Silurian  system  of  the  United  States,  are, 
however,  very  valuable.     As  examples,  we  may  mention  the  deposits  of  lead 
(galena)  found  in  the  Valley  of  the  Upper  Mississippi,  which  are  the  most 
remarkable  in  the  world ;  and  occur  in  that  division  of  the  Silurian  system 
known  as  the  Hudson  River  group.     The  rock  also  in  which  much  of  the 
native  copper  of  the  Lake  Superior  district  occurs  is  the  Potsdam  sandstone.  ' 

Most  of  the  salt  springs  of  the  United  States  issue  from  rocks  belonging  to 
the  Silurian  system ;  and  there  is  also  reason  to  believe  that  all  the  gold  of 
the  eastern  United  States  and  of  California  is  associated  with  metamorphic 
rocks  of  either  the  Silurian  or  Devonian  systems. 

DEVONIAN    SYSTE  M—  Old  Red- Sandstone. 

245.  This  system,  which  is  next  in  order  above  the 
Silurian,  derives  its  name — "  Devonian" — from  Devon- 

QUESTIOXB. — What  is  said  of  tho  thickness  of  the  rocks  of  the  Silurian  system  ?  What 
of  its  mineral  deposits?  What  system  is  next  in  order  above  the  Silurian?  l3y  what 
names  is  it  designated  ? 


*  The  student  who  desires  to  render  himself  better  acquainted  with  the  fossils  of  the 
Silurian  system,  as  developed  in  North  America,  will  find  detailed  descriptions  of  them, 
with  illustrations,  in  the  reports  of  the  geological  surveys  of  the  different  states  and  of 
Canada,  especially  in  the  reports  of  the  Geological  Survey  of  New  York.  At  the  State 
Geological  Hall,  at  Albany,  N.  Y.,  there  is  also  open  to  inspection  a  complete  collection 
of  the  fossils  themselves,  arranged  in  the  order  in  which  they  occur  in  the  different 
groups  and  beds  of  this  system,  and  conspicuously  labeled. 

In  inspecting  this  collection,  the  interest  of  the  observer  will  be  greatly  enhanced  if  he 


DEVONIAN     SYSTEM.  223 

shire,  in  England,  where  portions  of  it  are  especially  de- 
veloped. It  is  also  very  generally  known  as  the  u  Old 
Red- Sandstone,"  from  the  circumstance  that  in  Great 
Britain  and  other  localities  the  system  is  largely  made  up 
of  a' succession  of  sandstones  and  shales,  which  are  colored 
red,  by  the  presence  of  oxyd  of  iron. 

246.  Distribution, — The  Devonian  system,  like  the 
Silurian,  is  one  of  the  great  general  systems  of  the  strati- 
fied rocks,  and  there  are  few  regions  of  the  globe,  it  is  be- 
lieved, in  which  some  one  or  more  of  its  groups  do  not 
occur. 

In  Europe  it  is  very  extensively  developed ;  as  in  Great  Britain  (where  it 
has  been  made  celebrated  through  the  labors  of  Hugh  Miller) ;  in  France, 
Spain,  Belgium,  and  especially  in  Russia,  where  it  covers  at  least  150,000 
square  miles  of  surface. 

In  this  country  it  also  occupies  extensive  areas,  but  is  less  geographically 
extended  than  the  Silurian  system.  Its  greatest  development  occurs  in  the 
States  of  New  York  and  Pennsylvania ;  but  from  thence,  stretching  to  the 
west  and  southwest,  it  gradually  diminishes  in  thickness  and  ultimately  dis- 
appears. Devonian  rocks  are  also  known  to  exist  in  New  England,  in 
Canada  East,  and  in  the  more  northern  portions  of  the  continent. 

247.  Divisions  . — The  groups  and  subdivisons  of  the  rocks  of  the  Dev- 
onian system  recognized  in  New  York  are  as  follows,  proceeding  from  the 
highest  of  the  series  downward : 

Catskill  Group. 

Chemung  Group.,  Sandstone  of  Ohio. 

Portage  Group,    f 

Genesee  Slate. 

Hamilton  Group. 

Marcellus  Shale. 

Upper  Helderberg  Group. 

Cauda  Galli  Grit.     I 

Onskany  Sandstojic.l 

Fig.  141  is  an  ideal  section  representing  the  .divisions  of  the  rocks  of  the 
Devonian  system  in  North  America. 

QUESTIONS.— What  is  said  of  the  distribution  of  the  rocks  of  the  Devonian  system  ? 
What  of  it3  divisions  into  rocks  and  groups  ? 


considers  for  a  moment  the  great  antiquity  of  the  forms  before  him — an  antiquity  so 
vast,  that  the  period  representing  the  duration  of  the  human  race  upon  our  planet 
dwindles,  by  comparison,  into  an  insignificant  moment. 


224          FIEST    PRINCIPLES    OF     GEOLOGY. 

FIG.  141. 


1  2345678  <J  10 

1.  Upper  Silurian;  2.  Oriskany  Sandstone;  3.  Cauda  Galli  Grit;  4.  Upper  Helderberg 
Group ;  5.  Marcellus  Shale ;  6.  Hamilton  Group ;  7.  Genesee  Slate ;  S.  Portage  Group ; 
9.  Cheraung  Group ;  10.  Catskill  Group  ;  11.  Carboniferous  System. 

These  rocks  and  groups  of  the  Devonian  system,  although  mainly  named 
from  localities  in  the  State  of  New  York,  where  they  are  typically  developed 
and  have  been  especially  studied,  are  represented  by  equivalent  formations 
in  different  parts  of  the  country.  Thus,  the  0 risk-any  Group,  named  from 
Oriskany,  in  New  York,  extends  from  Southern  New  York  southwesterly  to 
Tennessee,  and  westerly  about  300  miles.  The  Chemung  and  Portage  Groups 
have  also  an  equal  extension.  Limestones  belonging  to  the  Upper  Helder- 
berg Group  are  widely  developed  throughout  the  Appalachian  chain  of 
mountains  south  of  the  Hudson  River,  and  westward,  both  in  the  United 
States  and  Canada.  The  Catskill  Group  is  principally  developed  in  New 
York  and  Pennsylvania,  and  forms  the  greater  portion  of  the  Catskill  moun- 
tains. Succeeding  the  Catskill  group  we  find  rocks  belonging  to  the  Car- 
boniferous system. 

248.  Characters , — In  New  York  and  Pennsylvania  the  rocks  of  the 
Devonian  system  consist  mainly  of  red,  brown,  and  gray  sandstones,  shales 
and  conglomerates,  with  some  limestones.      At  the  West,   the  equivalent 
rocks  are  for  the  most  part  limestones. 

249.  Life  of   the    Period   represented  by  the   Devonian 
System, — The  organic  remains  of  this  system,  though  often 
not  well  preserved  in  consequence  of  the  arenaceous  (sandy) 
nature  of  the  rocks,  are  nevertheless  of  high  and  increasing 
interest,  inasmuch  as  they  furnish  abundant  evidence  of 
terrestrial  vegetation,  as  well  as  distinct  traces  of  verte- 
brate life  upon  the  surface  of  our  planet. 

Plants, — As  already  stated,  the  fossil  plants  found  in  the  Silurian  sys- 
tem are  almost  exclusively  marine,  and  it  is  only  in  the  uppermost  strata — 
just  on  the  borders  of  the  Devonian  system — that  we  detect  any  traces  of 
a  terrestrial  vegetation.  As  we  ascend,  however,  into  the  overlying  system, 
tho  number  of  land  plants  gradually  increases.  At  the  same  time,  the  Dev- 
onian system,  as  a  whole,  is  not  fertile  in  plant  remains,  and  it  would  seem 
as  if  during  the  period  of  its  deposition,  the  vegetation  of  our  globe  was  con- 
fined to  a  few  detached  and  limited  areas. 

QUESTIONS.— What  is  the  character  of  the  rocks  composing  this  system  in  America? 
What  is  said  of  the  life  of  the  earth  during  tho  period  of  the  Devonian  system  ? 


DEVONIAN     SYSTEM.  225 

In  speaking,  moreover,  of  the  land  plants  of  these  ancient  times,  the  stu- 
dent should  also  understand  that  they  were  not  like  the  land  plants  commonly 
met  with  upon  the  surface  of  the  earth  at  the  present  day ;  but,  on  the  con- 
trary, judging  from  the  remains  we  find,  they  would  appear  to  have  belonged 
mostly  to  the  low  class  of  Acrogens  (§  195) ;  or,  in  other  words,  to  have  re- 
sembled our  ferns,  rushes,  sedges,  and  similar  plants  inhabiting  marshy 
localities.  Some  plants,  allied  to  the  Coniferous  or  Pine  family,  and  of  as 
high  an  organization,  would  also  appear  to  have  existed.  All  these  remains, 
however,  generally  occur  in  a«  fragmentary  and  carbonized  state,  as  if  they 
had  been  drifted  from  a  distance  upon  an  ocean  to  the  place  where  they  were 
deposited.  The  marine  plants  of  the  Devonian  system  are  similar  to  those 
found  in  the  Silurian.* 

Animals  . — In  the  Devonian  system,  the  same  forms  of  animal  life  that 
especially  characterize  the  Silurian  era — namely,  the  corals,  shel]s,  trilobites» 
etc. — are  continued,  and  in  some  of  its  groups  of  rocks  their  remains  are  very 
^abundant.  With  few  exceptions,  however,  the  fossils  of  the  Devonian  sys- 
tem are  of  different  species,  and  often  of  different  genera  from  those  of  the 
Silurian. 

But  the'  most  interesting  of  all  the  fossils  of  the-  Devonian  system  are  the 
fish,  which  occur  in  some  localities  in  such  abundance  that  the  rocks  seem 
to  form  one  great  cemetery  of  their  remains. 

The  first  indications  of  the  existence  of  fish  are  found,  as  has  been  already 
stated,  in  the  uppermost  rocks  of  the  Silurian  system ;  and  these — "  the  first- 
born of  their  family,  so  far  as  is  yet  known,"  all  belonged  to  the  order  of 
Flacoids  (See  §  201) — an  order  of  low  organization  and  ferocious  habits,  and 
of  which  the  dog-fish  and  the  sharks  are  the  best  living  representatives. 

"Some  of  these  old  Placoid  fishes,"  says  Hugh  Miller,  u  were  furnished  with 
strong  palates,  and  squat,  firmly-based  teeth,  well  adapted  for  crushing  the 
strong-cased  zoophytes  and  shells  of  the  period,  fragments  of  which  occur 
in  their  fecal  remains  (which  have  even  been  preserved  in  a  fossil  state) ; 
while  others  have  teeth  so  sharp,  thin,  and  deeply  serrated,  that  every  in- 
dividual tooth  resembles  a  row  of  poniards  set  up  against  the  walls  of  an 
armory ;  and  these  last,  says  Agassiz,  furnished  with  weapons  so  murderous, 
must  have  been  the  pirates  of  the  period." 

In  the  Devonian  system,  however,  an  entirely  new  order  of  fishes— -the 
Ganoids  (see  §  2M) — were  called  into  existence ;  while  tho  Placoids  of  the 
Silurian  era  continue  to  be  represented,  but  only  by  new  species,  the  former 

QUESTION'S. — What  is  known  of  its  vegetation  ?  What  is  said  of  the  animal  remains 
found  in  this  system?  What  are  its  most  interesting  fossils?  What  was  the  character 
of  the  first  created  fishes  ?  What  types  of  fishes  exist  in  the  Devonian  system  ? 


*  "A  distinguished  French  geologist,  M.  Brongniart,  has  shown  that  all  existing  marine 
plants  can  be  classified  with  regard  to  zones  of  climate— some  being  fitted  to  the  torrid 
zones,  some  for  the  temperate,  and  some  for  the  frigid.  And  he  establishes  the  fact  that 
the  marine  plants  of  these  early  times  indicate  a  tropical  climate,  although  they  may  be 
found  in  what  are  now  temperate  regions;  and  he  also  states,  that  those  of  the  higher 
rocks  betoken,  as  we  ascend,  a  gradually  diminishing  temperature." 

10* 


226       FIRST     PRINCIPLES     OF     GEOLOGY. 


species  of  this  order  having  previously  become  extinct.  And  from  this  epoch, 
says  Hugh  Miller,  during  the  times  of  the  Devonian,  Carboniferous,  Permian, 
Triassic,  and  Oolitic  systems — "a  period  comprising,  mayhap,  millions  of 
years" — all  fishes,  though  apparently  as  numerous,  individually,  as  they  are 
now,  belonged,  so  far  as  is  yet  known,  exclusively  to  these  two  orders. 

These  Ganoid  fishes  of  the  Devonian  system  were  characterized  by  some 
of  the  most  remarkable  and  peculiar  forms  that  have  ever  appeared  in  nature, 
and  in  some  species  it  is  at  first  difficult  to  see  any  resemblance  whatever 
to  a  fish.  Some  of  them  seem  to  form,  as  it  were,  a  connecting  link  between 
the  Crustacea  (crabs,  lobsters,  etc.)  and  the  true  fishes,  and  all  of  them  were 

FIG.  142, 


covered  over  with  hard,  enamelled  scales,  or  bony  plates,  and  not  unfre- 
quently  armed  with  sharp  fin-spines  of  bone.  Some  seem  to  have  been 
cased  in  a  complete  armature  of  solid  bone.  Hugh  Miller  describes  one 
species,  the  Pterichthys,  or  winged-fish  (Gr.,  Trrepov,  awing;  and  frfof,  a 
fish),  see  Fig.  142,  as  having  its  head  "covered  with  a  strong  helmet,  perfois 
ated  in  front  by  two  circular  holes,  through  which  the  eyes  looked  out;  its 
chest  protected  by  a  curiously  constructed  cuirass,  formed  of  plates,  and  the 

FIG.  143. 


tail  sheathed  in  a  flexible  mail  of  osseous  scales.     In  addition,  the  creature 
had  two  arms  or  wings,  that  combined  the  broad  blade  of  the  paddle  with 


QUESTIONS. — What  is  said  of  range  of  the  Placoid  and  Ganoid  fishes  ? 
character  of  the  Ganoid  fishes  of  the  Devonian  system? 


What  was  the 


DEVONIAN     SYSTEM.  227 

the  sharp  ^oint  of  a  spear,  and  served  both  for  propulsion  through  the  water 
and  as  weapons  for  defense.  Another  characteristic  fish  of  the  Devonian 
system,  the  Cephalaspis,  had  a  comparatively  small  elongated  body,  inserted 
within  the  cusp  of  a  large  crescent-shaped  head,  something  like  a  saddler's 
cutting-knife.  This  curious  head  was,  furthermore,  covered  on  the  upper 
side  with  a  hood,  or  single  large  plate  of  bone,  as  with  a  buckler ;  hence  the 
name,  implying  buckler -headed.  Fig.  143  represents  a  side  and  under  view 
of  one  species  of  the  Cephalaspis.  Similar  bone-bucklers,  which  covered  the 
head  of  another  Devonian  Ganoid — the  Asterolepis — have  been  found,  suffi- 
ciently large  "  to  cover  the  front  skull  of  an  elephant,  and  strong  enough  to 
have  resisted  a  musket  bullet."  Fig.  144  represents  a  curious  bone-plated 
Devonian  fish,  called  the  Coccosteus. 

FIG.  144. 


250.  Many  of  these  ancient  Ganoid  fish,  according  to  Prof.  Agassiz,  were 
invested,  to  some  extent,  with  the  characters  of  reptiles,  and  seem  to  have 
foreshadowed,  as  it  were,  the  existence  of  a  higher  class  of  animals,  long 
before  they  were  created.  Another  interesting  fact  noticed  respecting  these 
extreme  forms  of  Devonian  fishes,  is,  that  they  were  comparatively  short- 
lived, "as  if,"  says  Hugh  Miller,  "some  such  law  influenced  the  destiny  of 
genera  in  this  class  of  fishes,  as  that  which  we  find  so  often  exemplified  in 
the  human  species — namely,  that  the  giant,  the  dwarf,  or  deformed  person, 
is  seldom  a  long  liver."  Many  of  them  were  restricted  to  a  single  formation 
or  group  of  strata — appearing  for  the  first  time  in  the  lowest  deposits,  and 
becoming  extinct  with  the  uppermost.  In  many  instances  also,  they  appear 
to  have  all  died  at  once,  and  died  of  violence. 

"  "We  see  them  still  presenting,  over  wide  areas,  the  stiff  curved  outline— 
a  result  of  the  unequal  contraction  of  the  muscles— which,  as  in  the  case  of 
recently  netted  herrings,  indicates  that  dissolution  had  been  sudden. .  We 
find,  too,  that  their  remains  did  not  suffer  from  the  predatory  attacks  of  other 
fishes,  and  it  would  seem  as  if  all  the  finny  inhabitants  of  wide  tracts  of  sea 
had  been  at  once  cast  dead  to  the  bottom,  so  that  not  an  individual  survived 
to  prey  upon  the  remains  of  his  deceased  neighbors." — MILLER.  Such  phe- 
nomena clearly  indicate  the  occurrence  of  great  convulsions  of  the  sea-bottom 
during  this  ancient  period  of  the  earth's  history. 

251.  Reptiles,— In  the  strata  deposited  just  a  little  be- 
fore the  close  of  the  Devonian  system,  we  obtain,  for  the 

QUESTION.— What  new  class  of  animals  appears  for  the  first  time  in  this  system? 


228      FIRST     PRINCIPLES     OF     GEOLOGY. 

first  time,  evidence  of  the  existence  of  reptiles,  or  of  true 
air-breathing  animals  upon  the  surface  of  our  planet ;  just 
as  representatives  of  the  class  of  fishes  appear  for  the  first 
time  a  little  before  the  close  of  the  Silurian  system. 

FIG.  145. 


The  actual  remains  of  such  creatures  obtained  from  Devonian  rocks,  are 
thus  far  limited,  however,  to  a  very  few  specimens,  and  appear  to  have  been 
those  of  small  terrestrial  lizards,  or  animals  of  the  order  of  Batrachians  (frogs). 
Fig.  145  represents  the  best  preserved  specimen  of  a  Devonian  reptile  yet  dis- 
covered— the  Tderpeton  Elginense — a  creature  whose  existence  at  this  epoch 
indicates  the  presence  of  dry  lands  and  swampy  shores ;  in  all  likelihood  the 
same  shores  and  river-banks  on  which  grew  the  reeds,  ferns,  and  rush-liko 
plants  already  referred  to. 

In  addition  to  these  actual  remains,  the  tracks  or  foot-prints  impressed  by 
reptiles,  as  they  walked  over  the  muddy  or  sandy  shores  of  the  Devonian 
epoch,  have  also,  in  some  instances  been  very  perfectly  preserved,  and  now 
exist  in  the  consolidated  rock. 

252.  Economically,  the  products  of  the  Old  Red-Sandstone,  or  Devonian 
system,  are  neither  very  numerous  or  of  prime  importance. 

The  aggregate  thickness  of  the  strata  which  compose  the  system  in  this 
country  is  about  11,700  feet.  In  England,  the  thickness  of  the  entire  system 
has  been  estimated,  by  Sir  Roderick  Murchison.  at  10.000  feet;  and  as  these 
10.000  feet  include  (in  that  country)  three  formations  so  distinct  in  their 
groups  of  animal  life  that  not  one  species  of  fish  has  been  found  common  to 
both  the  higher  and  the  lower,  it  must  represent  in  the  history  of  the  globe 
an  enormously  protracted  period  of  time. 

QUESTION. — What  is  the  character  of  the  remains  of  these  animals?  What  is  said  of 
the  economical  products  of  the  Devonian  system  ?  What  of  the  thickness  of  its  strata  ? 


CARBONIFEROUS     SYSTEM.  229 


CARBONIFEROUS    SYSTEM. 

253.  This  system  is  next,  in  the  ascending  order,  above 
the  Old  Ked-Sandstone,  or  Devonian  system,  and  derives 
its  name  from  the  profusion  of  fossil  vegetation  found  in 
it — a  profusion  so  great,  that  it  not  only  forms,  in  many 
instances,  thick  seams  of  solid  coal  (coal  being  but  a  mass 
of  mineralized  vegetation),  but  also  enters  to  such  an  ex- 
tent into  the  composition  of  some  of  the  shales,  sandstones, 
and  limestones  of  the  system,  as  to  give  them  a  carboni- 
ferous or  coaly  aspect. 

254.  Distribution, — The  geographical  area  occupied  by  the  Carboni- 
ferous system  is  very  great,  and  there  are  but  few  regions  of  the  globe  in 
which  some  one  or  more  of  its  groups  of  rocks  do  not  occur.     The  countries 
in  which  those  portions  of  the  system  are  developed,  which  are  especially 
productive  of  coal,  will  be  hereafter  noticed  more  particularly. 

255.  Divisions, — Derived    from   the  waste  of   all  the 
previously  formed  rocks — the  granitic,  metamorphic,  Silu- 
rian, and  Devonian — the  strata  which  make  up  the  Car- 
boniferous system  necessarily  present  a  great  variety  and 
complexity  of  composition,  and  may  be  said  to  be  com- 
posed of  frequent  alternations  of  sandstones,  shales,  slates, 
and  limestones,  with  beds  of  coal  and  earthy  ores  of  iron. 

This  assemblage  of  strata  is  generally  separable  into  two  well-marked 
groups  or  formations,  which  differ  widely  from  one  another  as  respects  the 
nature  of  their  contained  fossils. 

The  lower  group  is  especially  characterized  by  the  presence  of  immense 
beds  of  limestone,  which  abound  to  a  most  wonderful  extent  in  marine  fossils 
— shells,  Crustacea,  corals,  crinoids,  fish,  etc. — and  have  evidently  been  de- 
posited at  the  bottom  of  a  tropical  ocean.  These  formations  of  limestone  are 
collectively  termed  the  "  Carboniferous"  or  "Mountain  Limestone;"  and  in 
some  localities  (as  in  the  "Western  States)  they  constitute  almost  exclusively 
the  lowest  division  of  the  rocks  of  the  Carboniferous  system,  while  in  others, 
they  are  associated  with,  or  (as  in  Pennsylvania)  almost  entirely  replaced  by 
conglomerates,  shales,  slates,  and  sandstones. 

QUESTIONS.— What  system  lies  next  in  order  above  the  Devonian  ?  Why  is  it  called 
the  Carboniferous?  What  is  said  of  its  distribution?  What  is  the  nature  of  the  rocks 
which  compose  the  Carboniferous  system  ?  How  may  they  be  generally  divided?  What 
are  the  characteristics  of  the  lower  group  ? 


230       FIRST     PRINCIPLES     OF     GEOLOGY. 

The  upper  group  of  the  Carboniferous  system,  from  the  circumstance  that  ifc 
contains  most  of  the  beds  or  seams  of  coal  existing  in  the  crust  of  the  earth, 
is  termed  the  "  Coal  Measures;"  and  consists  of  beds  of  sandstones,  shales, 
conglomerates,  limestones,  coal,  and  ores  of  iron,  alternating  irregularly. 
»  The  following  section  of  a  portion  of  the  upper  Carboniferous  rocks  of  Ohio 
well  illustrates  the  composition  of  the  coal  measures,  and  the  manner  in 
which  beds  of  coal  are  distributed  through  them : 

Sandstone. 

Coal,  6  feet  thick. 

Slaty  Sandstone,  50 

Bed  of  Iron  Ore,  1.5 

Sandstones,  To 

Coal,  3 

Dark  Bituminous  Shales,  4 

Sandstones,  80 

Iron  Ore,  1 

Sandstones,  SO 

The  sandstones  and  limestones  of  the  coal  measures  are  not  distinguish- 
able from  the  sandstones  and  limestones  in  the  lower  part  of  the  system. 
The  iron  ore  occurs  either  in  nodular  masses,  often  formed  around  some  or- 
ganic nucleus ;  or  as  a  clayey  (argillaceous)  carbonate  of  iron,  having  a  slaty 
structure ;  in  either  case,  however,  it  forms  comparatively  thin  beds,  associ- 
ated with  beds  of  shale.41'  The  beds  of  coal  vary  in  thickness  from  a  fraction 
of  an  inch  to  several  feet;  and,  in  some  instances,  beds  have  been  found 
measuring  forty  and  even  fifty  feet  in  thickness.  The  average  thickness  of 
workable  beds  of  coal  is  from  three  to  six  feet. 

The  characteristic  fossils  of  the  coal  measures  are  the 
remains  of  terrestrial  plants.  Marine  fossils  also  abound 
in  some  of  the  strata  ;  but  the  remains  of  land  plants  so 
predominate,  that  they  constitute  the  distinguishing  fea- 
tures of  the  formation,  and  everywhere  allow  its  easy  re- 
cognition. 

The  general  character  of  the  fossils  found  in  the  coal  measures  would  also 
indicate  that  the  sediments  which  inclose  them  were  not  of  exclusively  marine 

QUESTIONS. — What  of  the  upper  group  ?  What  are  the  coal  measures  ?  With  what 
rocks  are  beds  of  coal  usually  associated  ?  What  are  the  characteristic  fossils  of  the 
coal  measures  ? 


*  This  association  of  iron  ore  with  coal,  in  the  same  series  of  rocks,  is  a  matter  of  great 
practical  importance,  inasmuch  as  the  mineral  ore,  and  the  fuel  for  smelting  it,  are  thus 
brought  in  almost  absolute  contact  with  each  other.  The  coal  measures,  moreover, 
very  generally  furnish  the  limestone  (or  flux)  which  it  is  necessary  to  mix  with  the  iron 
ores  in  smelting  to  facilitate  their  fusion  ;  and  very  often  also  those  peculiar  clays  from 
which  fire-bricks  can  be  made  for  the  construction  of  furnaces.  In  Great  Britain,  nearly 
all  the  principal  mines  of  iron  that  supply  her  furnaces,  occur  in  the  coal  measures  ;  and 
their  product  of  ore  for  1S55  was  upward  of  nine  million  of  tons. 


CARBONIFEROUS     SYSTEM.  231 

origin,  but  rather  that  they  were  deposited  in  shallow  inland  seas,  fresh- 
water lakes,  or  the  estuaries  of  rivers.* 

256.  Condition  of  the  Earth  during  the  Epoch  repre- 
sented by  the  Carboniferous  System, — The  great  general 
features  of  the  earth's  surface,  during  the  deposition  of 
the  rocks  which  compose  the  Carboniferous  system,  can 
undoubtedly  be  made  out  by  geologists  with  a  high  degree 
of  accuracy. 

Thus,  during  the  epoch  which  represents  the  close  of  the  Devonian  and  the 
commencement  of  the  Carboniferous  system,  it  is  not  probable  that  any  very 
considerable  part  of  the  surface  of  our  planet  was  dry  land.  The  rocks  which 
were  deposited  at  this  time,  and  which  make  up  the  base  of  the  Carboni- 
ferous system,  are  mainly  limestones,  sandstones,  and  shales;  and  the  most 
superficial  observer  feels  as  little  difficulty  in  accounting  for  their  formation, 
as  he  would  in  accounting  for  the  origin  of  an  existing  coral  reef; — the  pro- 
fusion of  marine  fossils  contained  in  them  clearly  indicating  that  they  were 
deposited  at  the  bottom  of  an  ocean  swarming  with  animal  life.f 

At  a  later  epoch  of  the  Carboniferous  system,  the  causes  favorable  to  the 
so  abundant  production  of  limestone,  and  the  large  population  of  marine  ani- 
mals in  the  seas  in  which  it  was  deposited,  decline,  while  the  area  of  dry 
land  is  greatly  increased.  On  this  land  a  vegetation  flourished,  which  for 
rankness  and  abundance  cannot  probably  be  paralleled  by  the  most  favored 
tropical  locality  of  the  present  day ;  and  the  remains  of  which,  preseryed  and 

QUESTIONS. — What  information  do  the  fossils  of  the  coal  measures  impart  concerning 
tho  origin  of  the  sediments  that  inclose  them  ?  What  was  the  probable  condition  of  the 
earth  during  the  early  part  of  the  Carboniferous  epoch? 


*  The  arrangement  of  the  rocks  of  the  Carboniferous  system,  as  here  given,  into  Two 
groups,  is  exceedingly  general,  and  in  all  extensive  geological  treatises  the  reader  will 
find  that  more  exact  and  minute  divisions  are  recognized  and  referred  to.  By  the  Profs. 
Rogers,  who  have  devoted  much  attention  to  the  coal  formations  of  the  United  States, 
the  Carboniferous  system  is  divided  into  three  great  groups,  viz.,  the  Lower  Carboni- 
ferous, Middle  Carboniferous,  and  the  Coal  Measures.  The  European  geologists,  while 
dividing  the  Carboniferous  rocks  generally  into  two  series,  the  "Upper"  and  tho 
"  Lower,"  also  recognize  the  existence  of  three  well  marked  groups  of  strata,  viz.,  The 
Carboniferous  Slates,  forming  the  base  of  the  system ;  2.  The  Carboniferous,  or  Moun- 
tain Limestone  ;  3.  The  Coal  Measures.  In  Pennsylvania,  the  exact  divisions  of  the  Car- 
boniferous system  are  as  follows  :  3.  A  Conglomerate,  2,660  feet  thick,  resting  upon  rocks 
of  the  Devonian  system ;  2.  Carboniferous  Limestone,  or  Eed  Shales  and  Limestone, 
which  is  supposed  to  correspond  with  tho  Mountain  Limestone  of  Europe ;  3.  A  Con- 
glomerate, less  than  half  the  thickness  of  the  lower  division ;  4.  The  true  Coal  Measures. 

t  In  this  country  the  Lower  Carboniferous  limestones  are  most  extensively  developed  ; 
especially  in  the  western  States,  where  they  form  high  bluffs  along  many  of  the  rivers, 
and  also  abound  in  caves  or  caverns,  of  which  the  Mammoth  Cave  of  Kentucky  is  most 
remarkable.  In  the  northwestern  States  different  portions  of  this  formation  of  Car- 
boniferous limestone  receive  various  local  names:  such  as  the  Burlington  Limestone, 
Keokuk  Limestone,  St.  Louis  Limestone,  Kaskaskia  Limestone,  etc.,  etc. 


232       FIRST      PRINCIPLES     OF      GEOLOGY. 


covered  up  by  deposits  of  sediment,  now  constitute  the  great  coal  beds  of  our 
globe.  The  climate  of  the  earth,  during  the  Carboniferous  period,  even  in 
the  latitude  of  Bafiins  Bay  (coal  being  found  in  these  extreme  northern 
regions),  was,  undoubtedly,  similar  to  that  of  the  torrid  zone  ;  and  it  has  also 
been  thought  probable  that  the  atmosphere  contained  a  much  larger  propor- 
tion of  carbonic  acid  gas  (the  food  of  plants)  than  it  does  at  the  present  day. 

257.  Animal  Life  during  the  Carboniferous  Epoch, — Most 
of  the  families  of  invertebrate  animals  that  flourished  during  the  Devonian 
era  are  represented  in  the  Carboniferous  system — the  species,  and  with  few 
exceptions  the  genera,  being,  however,  different.  In  some  of  the  carboni- 
ferous limestones,  the  abundance  of  marine  shells  (univalves,  bivalves,  and 
chambered  shells)  is  quite  inconceivable  to  those  who  have  not  seen  them, 
and  their  remains,  cemented  into  rock  masses,  may  be  literally  said  to  form 
mountains.  The  corals,  too,  were  very  numerous  and  beautiful,  and  in  some 
instances  preserve  sufficient  of  their  former  color  to  impart  a  delicacy  of  tint 
to  ;the  marbles  containing  them :  while  the  patterns  of  their  structure  are 
also,  in  many  cases,  so  ornamental  and  varied,  as  to  suggest  their  employ- 
ment as  designs  for  calico  printing.  Figs.  14G  and  147  represent  the  patterns 
afforded  by  two  varieties  of  fossil  corals. 

FiG.  146.  FlG.  147. 


258.  During  this  period  of  the  earth's  history,  that  curious  family  of  radiate 
animals,  known  as  "  Crinoids"  "  Encrinites"  or  "  Stone  Lilies"  were  re- 
markably developed,  and  their  remains  may,  in  fact,  be  said  to  characterize 
the  Carboniferous  limestones,  in  the  same  manner  as  the  trilobites  are  especi- 
ally characteristic  of  the  Silurian  rocks,  and  the  bony-plated  fishes  of  the 
Devonian.  The  plan  upon  which  these  animals  were  constructed,  was  that 
of  a  cup- like  body  (something  like  the  calyx  of  a  lily),  furnished  with  numer- 
ous flexible  arms  or  branches,  and  attached  to  the  sea-bottom  by  a  jointed  and 
flexible  stalk,  or  column.  Fig.  29,  page  74,  represents  the  entire  extension- 
of  a  crinoid,  and  Fig.  148,  plates  1  and  3,  the  construction  of  the  bodies  of 
different  species,  with  their  attachment  to  their  supporting  columns.  The 

QUESTIONS.— What  was  the  probable  condition  of  the  earth  during  the  subsequent 
period  ?  What  types  of  invertebrate  animals  flourished  during  this  system  ?  What  is 
said  of  the  abundance  of  the  shells  and  corals  ?  What  class  of  invertebrate  animals  was 
particularly  abundant  during  the  Carboniferous  period  ? 


CAEBONIFEKOUS     SYSTEM. 


233 


stem  of  the  animal,  as  well  as  the  arms  which  radiated  in  every  direction 
from  its  body,  owed  their  flexibility  to  the  fact  that  they  were  composed  of 
an  amazing  number  of  little  bones,  all  articulated  together  like  the  vertebras 
of  the  spine,  and  variously  grooved  and  ornamented  on  their  surfaces.  Plates 
2  and  4,  Fig.  148,  represent  separate  joints  of  the  stems  of  crinoids. 


148. 


In  some  species,  the  number  of  arms  was  about  1,000,  and  the  number  of 
separate  little  bones  contained  in  them,  at  least  100,000;  yet  so  perfectly 
was  each  bone  articulated  with  its  neighbor,  and  so  firmly  were  the  whole 
bound  together  with  ligaments,  that  the  arms,  when  spread,  must  have  pos- 
sessed the  flexibility  and  tenacity  of  a  seine  of  stout  net-work.  "  Human 
ingenuity,  with  the  same  purposes  to  effect,  namely,  the  sweeping  of  shoals 
of  swarming  animals  into  a  central  receptacle,  would  probably  construct  a 
similar  machine ;  but  it  would  take  half  a  lifetime  to  build  one  equally 
elaborate." 

The  family  of  crinoids  are  represented  in  almost  all  the  rocks  of  the  geo- 
logical series,  from  the  Silurian  up  to  the  Tertiary  systems — 105  fossil  genera, 
each  of  which  includes  a  number  of  species — having  been  enumerated.  They 
appear  to  have  attained  their  greatest  development  in  the  Carboniferous 
system,  where  their  remains  form  almost  the  entire  mass  of  some  lime- 
stones. (See  Fig.  148,  plate  2.)  Two  genera  only  of  this  curious  family  are 
known  to  exist  at  the  present  day ;  and  specimens  of  these  are  by  no  means 
common. 

259.  The  ancient  fishes — the  Placoids  and  the  Ganoids — like  the  Crinoids, 
seern  also  to  have  received  their  fullest  development  during  the  Carboniferous 
epoch.  Their  number  was  very  great,  and  though  the  class  of  reptiles  had 
at  that  time  been  called  into  existence,  they  continued  to  retain,  till  the 
close  of  the  system,  a  marked  reptilian  character  and  organization.  The  fea- 
ture which  especially  impresses  an  observer  who  examines  their  remains  is 
the  formidable  character  of  the  offensive  weapons  with  which  they  were 
furnished,  and  the  amazing  strength  of  their  defensive  armature.  "The- 

QUESTION.— Describe  generally  the  structure  and  peculiarities  of  the  crinoids. 


234 


FIRST     PRINCIPLES     OF     GEOLOGY. 


teeth  of  one  species  of  these  ganoidal  fishes  (the  Rhizodus)  were  more  sharp 
and  trenchant  than  those  of  the  crocodile  of  the  Nile,  and  in  the  larger  speci- 
mens, fully  four  times  the  bulk  and  size  of  the  teeth  of  the  hugest  reptile  of 
this  species  now  living."  In  the  museum  of  the  Ivoyal  Society,  of  Edinburgh 
may  be  seen  the  remains  of  a  similar  reptilian  lish  from  the  Carboniferous 

Fro.  149. 


system,  which  was  probably  larger  than  any  true  fish  of  the  present  day, 
i.  e.,  from  thirty  to  forty  feet  in  length.  It  was  furnished  with  teeth  three 
times  larger  than  those  of  the  most  gigantic  living  alligator,  and  was  also 
covered  from  snout  to  tail  with  an  armor  of  enameled  bone,  that  must  have 
been  almost  impenetrable.* 

260.  From  the  very  perfectly  preserved  remains  that  have  been  found,  wo 
know  that  over  the  lakes  and  rivers  inhabited  by  the  reptilian  fishes  of  this 

QUESTION. — What  is  said  of  the  fishes  of  tlio  Carboniferous  system  ? 

*  "I  need  scarce  say,"  says  Hugh  Miller' (see  "  Testimony  of  the  Rocks"),  "  that  the 
geologist  finds  r.o  trace  of  that  golden  age  of  the  world  of  which  the  poets  delighted  to 
sing,  when  all  creatures  lived  together  in  unbroken  peace,  and  war  and  bloodshed  were 
unknown.  Ever  since  animal  life  began  upon  our  planet,  there  existed,  in  all  the  depart- 
ments of  being,  carnivorous  classes,  who  could  not.  live  but  by  the  death  of  their  neigh- 
bors, and  who  \verc  armed,  in  consequence,  for  their  destruction,  like  the  butcher  with 
Lis  axe  and  knife,  and  the  angler  with  his  hook  and  spear.  But  there  were  certain  pe- 
riods in  the  history  of  the  past,  during  which  these  weapons  assumed  a  more  formidabla 
aspect  than  at  others,  and  never  were  they  more  formidable  than  in  the  times  of  the  coal 
measures." 


CARBONIFEROUS     SYSTEM.  235 

period,  there  fluttered  several  species  of  insects,  furnished  with  broad,  gauze 
wings,  like  the  dragon  flies  (Devil's  Darning-Needles)  of  the  present  day. 
In  the  woods,  and  among  the  decaying  trunks  of  the  Carboniferous  trees, 
there  also  harbored  several  species  of  spiders  and  beetles,  and  with  these, 
large,  many-eyed  scorpions  and  cockroaches,  of  types  not  at  all  unlike  the 
existing  ones.  Fig.  149  represents  the  remains  of  a  fossil  scorpion,  from  the 
coal  rocks  of  Bohemia.  Not  an  insect,  however,  has  this  system  yet  pro- 
duced of  the  now  numerous  kinds  that  seek  their  food  among  flowers. 

The  remains  of  a  few  small  reptiles,  akin  to  frogs  and  lizards,  have  also 
been  found  in  the  Carboniferous  system. 

Among  the  Crustacea,  the  order  of  Trilobites,  so  numerous  and  varied  dur- 
ing the  preceding  systems,  was  represented  by  a  few  species  only,  that  can  be 
grouped  into  but  one  or  two  genera.  This  type  of  animal  was,  in  short, 
fading  away ;  and  with  the  close  of  the  Carboniferous  epoch  it  became  en- 
tirely extinct. 

261.  Vegetation  of  the  Carboniferous  System,— The 
forests  and  thickets  of  the  coal  period  included  no  species 
of  plants  now  known  upon  the  earth.  They  consisted 

FIG.  150. 


mainly  of  gigantic  shrubs,  which  are  either  not  represented 
by  any  existing  types,  or  are  akin  to  kinds  which  are  now 
only  found  in  small  and  lowly  forms.  The  land  upon 

QUESTIONS.— What  higher  types  of  animals  existed  ?    What  was  the  character  of  the 
vegetation  of  the  coal  period  ? 


236       FIRST     PRINCIPLES     OF     GEOLOGY. 

which  this  vegetation  flourished,  is,  moreover,  supposed  to 
have  been  flat  and  marshy,  and  only  slightly  elevated 
above  the  level  of  the  sea. 

The  remains  qf  nearly  900  species  of  terrestrial  plants  have  been  obtained 
from  the  strata  of  the  Carboniferous  system,  and  of  this  number,  at  least  two- 
thirds  belonged  to  the  low  order  of  Cryptogamia  (flowerless,  fruitless  plants — 
see  §  194) ;  a  proportion  which  would  probably  be  much  increased  if  we  were 
more  fully  acquainted  with  the  vegetation  of  this  epoch. 

FIG.  151. 


The  master  form,  or  type  of  the  era,  was  the  fern,  or  brake,  of  which  at 
least  250  species  have  been  already  obtained  frorn  the  coal  measures  of 
Europe.  The  fern  is  a  plant  which  thrives  best  in  warm,  shaded,  and  moist 
situations ;  and  in  tropical  countries,  where  these  conditions  abound,  there 
are  many  more  species  than  in  temperate  climes.  Some  of  the  family  are,  in 
the  present  tropics,  arborescent,  or  of  tree-like  size  and  shape  (sco  Fig.  150), 
and  on  the  islands  of  the  Indian  Archipelago,  and  in  Australia,  attain  not 
unfrequently  a  height  of  from  forty  to  fifty  feet.  Now,  many  of  the  ferns  of 
the  coal  measures  were  of  this  magnitude,  and  that,  too,  without  regard  to 
the  parts  of  the  earth  where  they  are  found.  In  the  Carboniferous  rocks  of 
Baffins  Bay;  of  Great  Britain;  of  Pennsylvania;  and  of  the  torrid  zone 


CARBONIFEROUS     SYSTEM. 


237 


alike,  fossil  arborescent  ferns  are  found,  thus  indicating  that  at  this  era  the 
present  tropical  temperature  existed  in  very  high  latitudes.  Fig.  151  repre- 
sents the  fossil  impression  of  a  fern  of  the  coal  period. 

In  the  swamps  and  ditches  of  the  temperate  zones  there  flourishes  an  in- 
ferior family  of  plants,  termed  Equisetacece ;  the  different  members  of  which 
bear  the  common  names  of  horse-tails,  cat-tails,  scouring  rush,  etc.,  etc. 
They  have  all  an  erect,  jointed  stem,  with  slender  leaves,  and  an  inflorescence 
at  the  top.  Now,  a  second  large  section  of  the  plants  of  the  Carboniferous 
era  were  of  this  kind,  but,  like  the  fern,  they  attained  the  magnitude  of 
trees.  While  existing  equiscta  rarely  exceed  three  feet  in  height,  and  the 
stems  are  generally  less  than  a  half  an  inch  in  diameter,  their  kindred,  en- 
tombed in  the  coal  beds,  seem  to  have  been  generally  fourteen  or  fifteen  feet 
high,  with  stems  from  six  inches  to  a  foot  in  thickness.  Arborescent  plants 
of  this  family,  like  the  arborescent  ferns, 
still  grow,  however,  in  tropical  countries. 

The  club-moss  family  (trailing  pine,  Ly- 
copodiacece)  are  other  plants  of  the  pres- 
ent surface,  usually  seen  in  a  lowly  and 
creeping  form  in  temperate  latitudes,  but 
presenting  species  which  rise  to  a  greater 
magnitude  (about  three  feet)  within  the 
tropics.  Many  species  of  this  family  are 
found  in  the  coal  beds,  "  and  it  is  thought 
that  they  have  contributed  more  to  the 
substance  of  the-  coal  than  almost  any 


FIG.  153. 


other  variety  of  plants.     But  like  the  ferns  and  equisc-taccce,  they  attained,  in 
the  coal  period,  a  gigantic  size.     The  kpidodendra  (so  the  fossil  genus  is 


238 


FIRST      PRINCIPLES      OF      GEOLOGY. 


called)  were  probably  from  forty  to  eighty  feet  in  height,  with  a  diameter 
at  the  base  of  three  feet,  and  a  leaf  full  twenty  inches  in  length.  The  exterior 
of  their  bark  was  scaly,  and  is  often  found  most  perfectly  preserved.  (See 

FIG.  134. 


FIG.  155. 


Fig.  152.)  Sometimes  the  gigantic  trunks  of  the  lepidodendra  are  found 
standing  upright  in  the  mine,  and  penetrating  successive  layers  of  sedimen- 
tary deposits.  (See  Fig.  153.) 

Fig,  154  represents  the  appearance  of  an  as- 
semblage of  great  fossil  trees,  as  they  ocean 
embedded  vertically  in  cliffs  of  carboniferous 
sandstone,  at  St.  Etienne,  in  France. 

The  other  loading  plants  of  the  coal  era  are 
Without  representatives  on  ihe  existing  sur- 
face of  the  earth,  and  their  characters  are,  iu 
genera],  less  clearly  ascertained.  Among  tho 
most  remarkable  -was  a  family  called  "  Siyil- 
laria,"  of  which  largo  trunks,  thirty,  sixty,  and 
even  seventy  feet  long,  are  abundant.  Theso 
trunks  were  probably  soft  and  pithy  in  the 
interior,  and  curiously  fluted  on  the  exterior 
surface,  with  leaves  attached  in  vertical  rows 
along  tho  flutings.  Fig.  155  represents  a  por- 
tion of  the  stem  of  one  species,  showing  the 
llutings,  and  tho  points  where  the  leaves  were 
attached. 

There  have  also  been  found  in  the  coal  meas- 
ures a  few  species  of  exogenous  plants,  wfiich 
probably  belonged  to  tho  pine  family,  and  appear  to  have  been  the  highest 
type  of  vegetation  which  existed  at  this  era.  Upon  sections  of  their  trunks, 


CARBONIFEROUS     SYSTEM.  239 

the  concentric  rings  of  annual  growth — a  record  of  the  changing  seasons  of 
these  ancient  years — are  still  clearly  traceable.* 

"Such  was  the  vegetation  of  the  Carboniferous  epoch — composed  of  forms 
at  the  bottom  of  the  botanical  scale — ilowerless,  fruitless,  but  luxuriant  and 
abundant  beyond  what  the  most  favored  spots  on  earth  can  now  show.  The 
rigidity  of  the  leaves  of  its  plants,  and  the  absence  of  fleshy  fruits  and  farina- 
ceous seeds,  unfitted  it  to  afford  nutriment  to  animals ;  and  monotonous  in  its 
Ibrms,  and  destitute  of  brilliant  coloring,  its  sward  probably  unenlivened  by 
any  of  tho  smaller  flowering  herbs,  and  its  shades  uncheered  by  music  of 
birds,  it  must  have  been  but  a  somber  scene  to  a  human  visitant.  But 
neither  man  nor  any  other  of  the  higher  animals  were  then  in  existence  to 
look  for  such  uses  or  such  beauties  in  this  vegetation.  It  was  serving  other 
and  equally  important  ends — clearing  (probably)  the  atmosphere  of  matter 
noxious  to  animal  life,  and  storing  up  mineral  masses,  which  were,  in  long- 
subsequent  ages,  to  prove  of  the  greatest  service  to  the  human  race,  even  to 
the  extent  of  favoring  the  progress  of  its  civilization." 

FIG.  156. 


&a&SsaiX;- 


•  Fig.  156  (designed  by  Sir  R.  I.  Murchison)  corivej-s  some  idea  of  the  prob- 
able character  and  appearance  of  the  vegetation  of  the  coal  period. 


*  The  shales  which  lie  immediately  above  the  beds  of  coal  afford  the  best  specimens  of 
coal  plants,  which  occur  between  every  succession  of  laminae.  The  display  of  interlacing 
stems  and  leaves  presented  by  a  newly  exposed  roof  of  a  coal  mine  is  thus  graphically 
depicted  by  Dr.  Buckland,  in  the  "  Bridgewater  Treatises :"— "  The  most  elaborate  imi- 
tations of  living  foliage  on  the  painted  ceilings  of  Italian  palaces  bear  no  comparison  with 
the  beauteous  profusion  of  extinct  vegetable  forms,  with  which  the  galleries  of  many  of 
our  coal  mines  are  overhung.  The  roof  is  covered  a;;  with,  a  canopy  of  gorgeous  tapestry, 
enriched  with  festoons  of  most  graceful  foliage,  flung  in  wild,  irregular  profusion  over 
every  portion  of  its  surface.  The  effect  is  heightened  by  the  contrast  of  the  coal  black 
color  of  these  vegetables  with  the  light  groundwork  of  the  rock  to  which  they  are  at- 
tached. The  spectator  feels  transported,  as  if  by  enchantment,  into  the  forests  of  another 
world ;  he  beholds  trees  of  form  and  character  now  unknown  upon  the  surface  of  the 
earth,  presented  to  his  senses  almost  in  the  beauty  and  vigor  of  their  primeval  life ;  their 
csaly  stems  and  bending  branches,  with  their  delicate  foliage,  are  all  spread  forth  before 
him,  little  impaired  by  the  lapse  of  indefinite  ages,  and  bearing  faithful  records  of  extinct 
systems  of  vegetation,  which  began  and  terminated  in  times  of  which  these  relics  are  the 


240          FIRST     PRINCIPLES    OF    GEOLOGY. 

262.  Formation  of  Coal,— It  is  now  universally  admitted 
by  geologists,  that  coal  is  a  mass  of  compressed,  altered, 
and  mineralized,  vegetation,  just  as  sandstone  is  con- 
solidated sand,  and  slate  and  shale  consolidated  clay  or 
mud. 

The  evidence  upon  which  the  belief  is  founded  may  be 
briefly  stated,  as  follows  : 

1st.  The  enormous  profusion  of  fossil  plants,  in  the 
form  of  impressions  of  leaves,  trunks,  branches,  and  barks 
of  trees,  found  in  immediate  connection  with  coal  seams. 
2d.  Coal  is  composed  of  carbon,  hydrogen,  and  oxygen, 
the  same  elements  (though  differing  in  proportion)  which 
enter  into  the  composition  of  plants.  3d.  The  substance 
of  coal,  when  examined  under  the  microscope,  affords 
unmistakable  evidence  of  a  vegetable  (cellular)  struc- 
ture. 4th.  All  the  stages  of  gradation  between  perfect 
wood  and  perfect  coal  may  be  traced  with  the  greatest 
certainty. 

But  granting  the  vegetable  origin  of  coal,  the  question  immediately  sug- 
gests itself:  Under  what  circumstances  could  so  great  an  amount  of  vegetable 
matter  have  ever  accumulated  ? — the  magnitude  of  which  may  be  realized 
in  a  degree,  from  the  asserted  fact  "that  all  the  forests  of  the  United  States, 
if  gathered  into  one  heap,  would  fail  to  furnish  the  materials  of  a  single  coal 
seam  equal  to  that  of  Pittsburg,  Penn. " 

Furthermore,  coal  is  found  stratified,  laminated,  and  extended,  in  horizon- 
tal beds,  which  often  cover  very  large  areas,  with  a  nearly  constant  thickness 
— the  great  Pittsburg  coal  seam,  above  referred  to,  for  example,  having  a 
nearly  uniform  thickness  of  from  eight  to  twelve  feet,  and  is  estimated  to 
have  once  covered  a  surface  of  90,000  square  miles.  Coal,  moreover,  is 
ordinarily  encased  between  beds  of  shale  or  sandstone,  which  bear  evident 
proof  of  having  been  slowly  deposited  in  quiet  waters.  In  some  coal  fields, 
as  many  as  seventy  seams  of  coal,  varying  in  thickness  from  a  few  inches  to 
four,  six,  eight,  ten,  twelve,  and  twenty  feet,  occur  thus  interstratified  with 
shales  and  sandstones ;  and  yet,  notwithstanding  these  frequent  alternations 

QUESTIONS.— What  are  the  principal  reasons  which  induce  belief  that  coal  has  resulted 
from  an  accumulated  vegetation?  What  is  said  of  the  vastness  of  such  accumulations? 
Under  what  conditions  is  coal  found  ? 


infallible  historians.  Such  are  the  grand  natural  herbaria,  wherein  these  ancient  re- 
mains of  the  vegetable  kingdom  are  preserved  in  a  state  of  integrity  little  short  of  their 
living  perfection,  under  conditions  of  our  planet  which  exist  no  more." 


CARBONIFEROUS     SYSTEM.  241 

of  material,  the  purity  of  the  coal  is  such,  that  it  rarely  contains  any  con- 
siderable admixture  of  mud,  sand,  or  other  foreign  mineral  substances.* 

In  explanation  of  these  phenomena,  various  hypotheses  have  been  sug- 
gested, but  the  general  opinion  of  the  best  geologists  of  the  present  day  is, 
that  the  vegetable  matter  constituting  coal,  must,  in  the  main,  have  grown 
and  accumulated  in  immense  jungles  and  peat  mosses  for  many  years ;  that 
the  land  must  have  then  sunk,  and  become  the  basin  of  a  lake  or  estuary, 
into  which  rivers  carried  mud  and  sand ;  these,  covering  the  vegetable 
matter,  gradually  consolidated  into  shales  and  sandstones,  while  the  vege- 
table matter  itself  underwent  the  process  of  mineralization,  and  was  con- 
verted into  coal.  This  being  done,  it  is  supposed  that  the  area  of  deposit 
was  again  elevated,  so  as  to  become  once  mere  the  scene  of  luxuriant  vege- 
tation ;  then  again  submerged,  and  overlaid  by  new  deposits  of  sandstone 
and  shale ;  then  once  more  elevated  and  covered  with  plants,  and  again  sub- 
merged ;  and  these  alternations  of  submergence  and  elevation  are  presumed 
to  have  taken  place  as  often  as  there  are  beds  of  coal  in  any  particular  coal 
field."f 

QUESTIONS. — What  theory  of  the,  formation  of  coal  is  at  present  adopted  by  most  geolo- 
gists? 


*  The  student  will  not  fail  to  observe  a  striking  difference  in  the  modes  of  occurrence 
of  mineral  ores  and  coal.  The  former  exist  in  the  form  of  veins  intersecting  the  strata ; 
the  latter,  in  the  form  of  seams  parallel  with  the  strata.  The  former  extend  indefinitely 
downward;  the  latter  horizontally.  "Ignorance  of  this  simple  but  radical  difference 
has  been  the  cause  of  much  pecuniary  loss.  When,  for  instance,  some  years  since,  it  was 
rumored  in  Philadelphia  that  the  bottom  of  one  of  the  great  Pennsylvania  mines  had  been 
reached,  there  was  a  panic  in  the  market,  and  the  price  of  stocks  in  coal  mines  declined 
enormously — from  a  lack  of  knowledge  of  the  fact,  that  the  continuation  of  coal  scams 
was  to  be  looked  for  horizontally  rather  than  vertically."  In  some  instances,  where  the 
rocks  of  the  Carboniferous  system  have  been  elevated  into  vertical  positions,  the  coal 
seams  may  appear,  like  metallic  veins,  to  extend  downward  ;  but  in  all  such  cases  it  will 
be  observed  that  the  coal  beds  are  strictly  parallel  with  strata,  and  have  been  elevated 
with  them.  This  phenomenon  is  illustrated  by  the  accompanying  sketch  (Fig.  1ST)  of  the 
anthracite  coal  fields  of  Pennsylvania. 


t  "  This  sinking  process,  though  persistent  in  the  main,  must  have  been  of  an  inter- 
mittent and  irregular  kind.  In  some  instances,  forests  seem  to  have  grown  on  vast  plat- 
forms,  that  retained  their  level  unchanged  for  centuries — nay,  thousands  of  years  to- 
gether ;  in  other  cases,  the  submergence  seems  to  have  been  sudden,  and  to  such  a  depth, 
that  the  sea  rushed  in  and  occupied  wide  areas  where  the  land  had  previously  been,  and 
this  to  so  considerable  a  depth,  and  for  so  extended  a  period,  that  the  ridges  of  coral  which 
formed,  and  the  forests  of  Encrinites  which  grew,  in  these  suddenly  hollowed  seas, 
formed  thick  beds  of  limestone,  which  we  now  find  interstratified  with  coal  beds,  shales, 
and  sandstones.  Then  succeeded  an  upward  movement,  and  the  same  area  which  had 
been  first  occupied  by  a  forest,  and  then  by  a  lake  or  sea,  came  to  be  occupied  by  a  forest 
again  ;  and  though,  of  course,  mere  deposition  of  mud  and  sand  might  have  filled  up  the 
lake  or  sea  to  the  level  of  the  water,  it  is  not  easy  to  conceive  how,  without  positive  up- 

11 


242        FIRST     PRINCIPLES     OF     GEOLOGY. 

263.  Climatic  conditions  of  the  Carboniferous  Era, — There 
is  one  circumstance  in  connection  with  the  formation  of  coal  which  has  given 
rise  to  a  vast  amount  of  ingenious  speculation  and  hypotheses,  viz. :  the  ap- 
parent sameness  of  external  conditions  over  such  extensive  areas  of  the  earth 
as  are  now  occupied  by  our  known  coal  fields.  Thus,  the  same  gigantic 
ferns  and  club-mosses  are  found  alike  in  the  coal  fields  of  America,  Europe, 
Melville  Island,  Greenland,  and  Australia — regions  widely  separated,  and  at 
once  tropical,  temperate,  and  frigid.  To  account  for  this  luxuriance  and 
homogeneity  of  vegetable  growth  various  causes  have  been  suggested,  as  the 
earth's  central  heat,  a  change  in  the  earth's  axis,  a  larger  percentage  of  car- 
bonic acid  in  the  atmosphere,  the  planetary  system  moving  through  warmer 
regions  of  space,  and  the  like ;  but  thus  far  geologists  have  arrived  at  no 
definite  conclusions  upon  the  subject. 

Deposits  of  carbonaceous  matter  have  occurred  at  almost  every  period  of 
the  earth's  history,  as  is  evidenced  by  the  fact  that  thin  seams  of  coal  are 
found  in  almost  all  the  geological  systems ;  but  the  coal  beds  which  admit 
of  economical  working  are  almost  exclusively  confined  to  the  Carboniferous 
system.  The  only  exceptions  are  a  few  coal  fields  belonging  to  the  Oolitic 
or  Jurassic  system,  which,  in  Virginia  and  somo  other  localities,  admit  of 
profitable  mining.*  It  seems,  therefore,  certain,  that  whatever  may  have 
been  the  conditions  which  allowed  of  so  abundant  a  terrestrial  vegetation  at 
this  particular  epoch  of  the  earth's  history,  those  conditions  ceased  about  the 
time  when  the  era  of  the  Carboniferous  system  terminated.  A  high  tempera- 
ture was  evidently  not  one  of  these  conditions,  for  there  are  evidences  of 
it  afterwards;  and  some  authorities  incline  to  the  belief  that  the  super- 
abundance of  carbonic  acid  gas,  which  is  supposed  to  have  existed  during 
this  era,  was  expended  before  its  close.  "  There  can  be  no  doubt  that  the 
infusion  of  a  large  amount  of  this  gas  into  the  atmosphere  at  the  present  day 
would  be  attended  by  precisely  the  same  circumstances  as  in  the  time  of  the 
coal  epoch.  The  higher  forms  of  animal  life  would  not  have  a  place  on 
earth.  Vegetation  would  be  enormous ;  and  coal  strata  would  be  formed 
from  the  vast  accumulations  of  woody  matter,  which  would  gather  ia  every 
favorable  locality." 

QUESTION. — What  arc  supposed  to  have  been  the  climatic  conditions  of  the  earth  during 
this  period? 

heaval,  for  at  least  a  few  feet,  such  surfaces  at  the  water  level  should  have  become  suffi- 
ciently consolidated  for  the  production  of  the  gigantic  coal  vegetation.  But  the  sinking 
condition  was  the  general  one.  Platform  after  platform  disappeared,  as  century  after 
century  rolled  away,  impressing  upon  them  their  character  as  they  passed  ;  and  so  the 
coal  measures,  where  deepest  and  most  extensive,  consist,  from  bottom  to  top,  of  these 
buried  platforms,  ranged  like  the  sheets  of  a  work  in  the  course  of  printing,  that,  after 
being  stamped  by  the  pressman,  are  then  placed  horizontally  over  one  another  in  a  pile." 
—Hugh  Miller. 

*  The  knowledge  of  this  simple  fact  would  have  saved  the  useless  expenditure  of  thou- 
sands of  dollars  both  in  this  country  and  in  Europe.  It  is  worse  than  useless  to  expend 
money  and  labor  in  following  up  signs  of  coal,  unless  we  are  sure  we  zire  upon  strata  of 
the  Carboniferous  system. 


CARBONIFEROUS     SYSTEM. 


243 


264.  The  termination  of  the  Carboniferous  system  is  marked  by  evidences 
of  volcanic  violence.  Coal  beds  generally  lie  in  basins,  as  if  following  the 
curve  of  the  beds  of  lakes  or  seas.  But  there  are  few  basins  which  have  not 
been  broken  up ;  some  portions  of  them  being  tossed  up  on  edge,  while 
others  have  been  allowed  to  sink  ;  thus  causing  the  ends  of  strata  to  be  re- 
moved many  yards,  or  even  hundreds  of  feet,  from  the  corresponding  ends 
of  neighboring  fragments.  Fig.  158  illustrates  the  nature  and  mode  of  oc- 
currence of  such  disturbances  (A,  B,  and  C  representing  three  seams  of  coal). 
These  phenomena  are  held  to  have  been  the  results  of  volcanic  movements 
below,  the  operation  of  which  is  further  seen  in  numerous  dikes  and  in- 
trusions of  trap  rock,  which  traverse  the  coal  measures  in  every  direction. 

FIG.  158. 


Fig.  159  represents  a  section  of  the  coal  fields  of  Belgium,  and  conveys  an 
idea  of  the  manner  in  which  coal  seams  and  their  encasing  strata  of  shales, 
sandstones,  and  limestones  are  often  flexed,  and  apparently  multiplied.  Fig. 
157  represents  a  section  of  the  anthracite  coal  fields  of  Pennsylvania. 

Fia.  159. 


Such  disturbances,  although  often  very  annoying  to  the  miner,  have,  how- 
ever, on  the  whole,  facilitated  the  discovery  and  working  of  coal,  by  causing 
a  succession  of  beds  to  outcrop,  or  appear,  at  the  surface.  Figs.  158  and 
159  also  show  the  manner  of  reaching  and  working  the  different  coal  seams 
by  a  system  of  shafts  and  subterranean  galleries.* 

QUESTION. — What  phenomena  marked  the  termination  of  tho  Carboniferous  system? 

*  Over  a  large  part  of  the  United  States  it  has  not  become  necessary  to  sink  shafts  for 
coal  to  any  very  great  depth,  but  the  quarrying  is  commenced  at  the  outcrop  of  the  coal 
bed  ;  and,  till  the  cover  becomes  of  very  considerable  thickness,  it  is  found  economical  to 
"strip"  off  the  overlying  rock  rather  than  to  excavate  an  underground  gallery.  In 
Great  Britain,  however,  the  excavations  for  coal  constitute  some  of  the  deepest  mines  in 
the  world— i.  e.,  1,500, 1,800,  and  2,000  feet.  And  in  one  of  these  deep  pits  in  Scotland,  403 
feet  below  the  surface,  Hugh  Miller  tells  us  he  has  seen  the  rock  roof  of  a  gallery  com- 
pletely covered  with  impressions  of  the  feet  of  a  reptile  that  walked  over  it,  ages  ago, 
when  it  formed  the  immediate  (muddy)  terrestrial  surface. 


244      FIRST     PRINCIPLES     OF     GEOLOGY. 

Other  proofs  of  violence  during  the  Carboniferous  epoch  are  seen  in  the 
existence  of  great  beds  of  conglomerates,  which  occur  in  this  system.  In 
Pennsylvania  two  such  great  formations  have  been  observed — one  near  the 
base  of  the  system,  2,660  feet  thick;  the  other  higher  in  the  series,  and  of 
about  one  half  this  thickness.  Now,  these  conglomerates,  as  usual,  consist 
of  fragments  of  older  rocks,  more  or  less  worn  from  being  tumbled  about  in 
agitated  water,  and  laid  down  in  a  mud  paste,  which  afterward  hardened. 
'We  may  legitimately  infer,  that  volcanic  disturbances  broke  up  the  older 
rocks,  that  their  fragments  were  worn  in  seas ;  and  subsequently  deposited 
with  finer  particles,  in  layers. 

The  close  of  the  Carboniferous  system  was  also  characterized  by  the  passing 
away,  or  destruction  of  many  forms  of  organic  life  previously  nourishing — 
especially  in  the  vegetable  kingdom. 

265.  Varieties   of  Coal. — Wood,   and  in   fact  all  vegetable  tissues, 
consist  essentially  of  carbon,  hydrogen,  and  oxygen,  combined,  in  very  nearly 
equal  chemical  proportions.     If  we  abstract  from  wood  a  large  proportion  of 
its  oxygen,  and  compress  the  remaining  constituents  until  they  become  dense 
and  compact,  the  product  formed  will  differ  in  no  respect  from  the  more  in- 
flammable varieties  of  coal. 

Now,  when  accumulations  of  vegetable  matter  are  buried  in  the  earth,  un- 
der favorable  circumstances,  and  decomposition  ensues,  with  an  entire  or 
partial  exclusion  of  air,  a  similar  result  is  produced  naturally ;  or,  to  spoak 
more  precisely,  a  large  proportion  of  the  oxygen,  and  a  small  proportion  of 
the  hydrogen  of  the  vegetable  tissues  separate,  and  leave  behind,  as  a  resi- 
due, substances  rich  in  carbon  and  hydrogen — hydrocarbons,  as  they  are 
technically  called.  These,  variously  affected  by  pressure,  or  by  heat  and 
pressure  combined,  furnish  all  the  different  varieties  of  coal. 

266.  Peat  (see  §  163)  may  be  regarded  as  coal  in  its  incipient  stage  of 
formation,  and,  if  submerged  and  covered  to  great  depths  with  strata,  would, 
undoubtedly,  in  time,  become  true  coal.     As  it  is,  the  layers  of  ancient  peat, 
obtained  from  the  bottom  or  interior  of  peat  bogs,  can  hardly  be  distinguished 
from  coal,  and  constitute  an  excellent  fuel. 

267.  Two  principal  varieties  of  mineral  coal  are  recog- 
nized— bituminous  and  anthracite. 

Bituminous  coal  may  be  considered  as  a  mechanical 
mixture  of  carbon  and  bitumen — the  last  being  a  some- 
what general  name  for  certain  compounds  of  carbon  and 

QUESTIONS.— What  is  the  present  condition  of  most  coal  beds?  What  is  said  of  the  ex- 
istence of  beds  of  conglomerates  in  this  system  ?  What  is  the  chemical  composition  of 
wood?  How  may  wood  be  theoretically  converted  into  coal?  How  ia  vegetable  matter 
actually  changed  into  coal?  What  relation  is  sustained  by  peat  to  coal?  What  two 
principal  varieties  of  coal  are  recognized  ?  What  ia  the  composition  of  bituminous  coal? 


CARBONIFEROUS     SYSTEM.  245 

hydrogen,  the  products  of  the  decomposition  of  vegetable 
(or  animal)  substances,  which  resemble  common  tar  or 
pitch,  and  are  highly  inflammable. 

If  we  conceive  a  piece  of  charcoal  thoroughly  impregnated  with  pitch  or 
tar,  we  should  have  a  substance  very  similar  to  bituminous  coal. 

These  two  ingredients  of  coal  are  easily  separated  from  one  another  by 
heat,  as  is  constantly  done  in  the  manufacture  of  illuminating  gas ;  the  more 
volatile  bitumen  being  driven  off  from  the  coal  in  the  form  of  gas,  or  collect- 
ing in  the  pipes  as  coal  tar,  while  the  carbon  or  coke  remains  behind. 

Anthracite  is  the  name  given  to  a  coal  whose  bitumin- 
ous or  volatile  constituents  have  been  mainly  driven  off 
by  the  agency  of  heat  and  pressure,  leaving  the  carbon  in 
a  dense  and  nearly  pure  condition  behind. 

"When  bituminous  coal  is  ignited,  its  volatile  constituents,  expelled  by 
heat,  burn  with  flame  and  smoke ;  while  anthracite,  from  its  previous  de- 
privation of  bitumen,  burns  without  flame  or  smoke. 

Between  these  two  extremes,  coal  is  found  of  almost  every  intermediate 
variety.  The  richest,  or,  as  they  are  technically  termed,  the  "  fattest"  bitu- 
minous coals  contain  from  forty  to  sixty  per  cent,  of  bituminous  matter. 
Cannel  (candle)  coal  is  a  highly  compact  variety  of  bituminous  coal  of  an  even 
texture,  and  breaks  with  a  conchoidal  or  shell-like  fracture.  It  contains  a 
large  amount  of  volatile  matter,  and,  when  lighted,  burns  freely  like  a  candle 
— hence  its  name.  Jet  is  an  extreme  variety  of  cannel  coal,  of  deep  black 
color  and  brilliant  luster ;  it  is  capable  of  receiving  a  high  polish,  and  is  often 
sot  as  jewelry. 

268.  The  purest  coals  yield,  on  combustion,  only  one  or  two  per  cent,  of  ash, 
or  incombustible  matter ;  ordinary  coals,  however,  yield  from  five  to  ten  per 
cent. — an  amount  that  corresponds  very  nearly  with  the  quantity  of  saline 
and  earthy  substances  found  in  the  tissues  of  plants ;  others  more  impure 
may  contain  twenty,  thirty,  or  fifty  per  cent,  of  ash.  At  this  last  point  coal 
loses  the  property  of  ready  combustion,  and  also  the  name  of  coal,  and  be- 
comes carbonaceous,  or  bituminous  shale  or  slate.* 

QUESTIONS. — Illustrate  the  composition  of  bituminous  coal  ?  What  is  anthracite  ?  Why 
does  bituminous  coal  burn  with  flame  and  smoke  ?  Why  does  anthracite  burn  -without 
flame  and  smoke  ?  What  is  said  of  the  other  and  intermediate  varieties  of  coal  ?  What 
is  jet  ?  What  amount  of  Impurity  usually  exists  in  coal  ? 


*  Sulphuret  (sulphide)  of  iron  often  occurs  intermingled  with  coal,  and  when  present 
in  considerable  quantity  is  a  most  deleterious  impurity ;  inasmuch  as  the  sulphurous 
acid  gas,  generated  from  it,  is  not  only  noxious,  but  also  rapidly  corrodes  the  iron  work 
of  the  stoves  and  furnaces  with  which  it  comes  in  contact.  When  exposed  to  air  and 
moisture,  sulphuret  of  iron  undergoes  decomposition,  and  develops  heat ;  and  bitumin- 
ous coals  containing  it,  are,  for  this  reason,  always  liable  to  spontaneous  combustion. 


246        FIRST     PRINCIPLES     OF     GEOLOGY. 

Anthracite  coal  may  be  regarded  as  a  metamorpliic 
coal ;  and  is  rarely  found  except  in  regions  very  much 
disturbed  by  igneous  agency,  and  where  the  strata  are 
inclined,  broken,  and  contorted. 

It  often  happens,  moreover,  that  in  the  same  coal  field  the  coal  is  anthracite 
or  bituminous,  according  as  the  strata  are  more  or  less  disturbed  and  altered. 
Thus,  in  Eastern  Pennsylvania,  where  the  coal  strata  are  very  much  con- 
torted and  sometimes  perpendicular  (see  Fig.  157),  the  coal  is  all  anthracite; 
while  in  Western  Pennsylvania,  where  the  strata  are  nearly  horizontal,  the 
coal  is  bituminous.  In  New  England  coal  occurs  associated  with  strata  that 
have  been,-  subjected  to  an  extreme  degree  of  metamorphism,  or,  in  otEer 
words,  "have  been  more  acted  upon  and  hardened  by  heat  than  usual," 
and  here  the  coal  is  rendered  so  stony,  and  approaches  so  closely  in  charac- 
ter to  graphite  or  black  lead,  that  it  is  rendered  nearly  (or  quite)  unfit  for  fuel. 

269.  G  r  a  p  h  i  t  e  (Plumbago,  or  Black-Lead)  is  generally  believed  to  be 
anthracite  coal,  which  has  been  subjected  to  the  most  extreme  degree  of 
mineralization  or  metamorphism.    It  occurs  chiefly  in  the  older  geological  sys- 
tems— very  frequently  in  the  neighborhood  of  igneous  eruptions.     It  consists 
almost  entirely  of  pure  carbon,  with  a  small  proportion  of  iron,  as  an  admixture. 

270.  Mineral   Oils  (Naphtha,  Petroleum),  Asphaltum,   etc  ,— When 
bituminous  coal,  or,  in  fact,  any  substance  of  vegetable  or  animal  origin, 
which  is  rich  in  carbon  and  hydrogen,  is  subjected  to  heat  in  close  vessels, 
certain  volatile  constituents  distill  over,  and,  on  condensation,  yield  gas  (car- 
bureted hydrogen),  oils,  and  various  pitch-like  products.       This   result  which 
is  extensively  produced  in  the  arts,  for  the  manufacture  of  gas,  coal  oils,  etc,, 
appears  to  have  taken  place  naturally  and  on  a  large  scale,  in  the  earth  ;  and 
we  accordingly  find,  in  some  localities,  emanations  of  inflammable  gas  (see 
§  146) ;  or  springs  of  mineral  oil  (the  thinner  varieties  of  which  are  termed 
"Naphtha,"  and  the  more  viscid,  "Petroleum"} ;  or  hardened  masses  of  pitchy 
matter,  which  are  known  as  "Asphaltum,"  "Mineral  Pilch,''1  "Bitumen"  etc. 

The  product  of  natural  oil  springs  is  often  very  abundant.  In  Burmah, 
Asia,  a  single  group  of  springs  are  said  to  yield  regularly  400,000  hogsheads 
of  petroleum  annually.  In  the  United  States  large  supplies  of  mineral  oils 
are  obtained  in  many  localities — especially  in  "Western  Pennsylvania  and 
Virginia.  In  Venango  County,  Penn.,  where  the  oil  is  bored  for  as  in  the 
construction  of  Artesian  wells,  subterranean  reservoirs  have  been  struck, 
which  are  reported  to  have  yielded  from  400  to  800  gallons  daily. 

The  most  remarkable  accumulation  of  bituminous  matter  known,  is  tho 
Great  Pitch  Lake  of  Trinidad,  "VYest  Indies,  which  is  three  miles  in  circum- 
ference, and  of  an  unknown  depth.  It  appears  to  be  an  immense  deposit  of 
petroleum,  partially  dried  and  hardened  by  exposure  to  the  atmosphere. 

Mineral  oils  and  bitumen  are  not,  as  might  be  supposed,  tho  product  of 
Carboniferous  rocks  exclusively;  but,  on  the  contrary,  they  are  yielded  by 

QUESTIONS.— Under  what  circumstances  is  anthracite  coal  found  ?  What  are  illustra- 
tions of  its  occurrence?  What  is  graphite,  or  plumbago  ?  What  is  said  of  the  origin  of 
the  natural  oils  ?  Where  is  the  most  remarkable  natural  accumulation  of  bitumen  ? 


CARBONIFEROUS     SYSTEM.  247 

strata  of  almost  every  age  which  are  rich  in  tho  remains  of  plants  or  ani- 
mals. In  tin's  country  some  of  the  most  copious  oil  springs  (i.  e.,  those  of 
Pennsylvania)  come  up  through  strata  which  are  older  than  tho  Coal  Meas- 
ures, and  which  are  almost  barren  of  fossil  plants. 

271.  Distribution  of  Coa  1. — Coal  is  very  widely  distributed  over  tho 
world,  although  some  countries  are  more  highly  favored  than  others.  Avail- 
able coal  fields  occur  in  Great  Britain ;  in  Spain,  France,  Belgium,  and  Middle 
Europe ;  in  India,  China,  and  Japan ;  in  the  islands  of  the  Indian  Archi- 
pelago; in  Australia  and  New  Zealand;  in  South  America,  Chili,  and  Peru; 
in  Greenland,  Melville  Island,  and  in  British  America.  But  nowhere  is  the 
coal  formation  more  extensively  displayed  than  in  the  United  States,  and 
nowhere  are  its  beds  of  greater  thickness,  more  convenient  for  working,  or 
of  more  valuable  quality. 

The  eastern  half  of  tho  continent  of  North  America  exhibits  five  great 
coal  fields,  extending  from  Newfoundland  to  Arkansas :  1.  The  first,  or  most 
eastern,  is  that  of  tho  British  Provinces,  Newfoundland,  Nova  Scotia,  and 
New  Brunswick.  Its  area  is  probably  about  9,000  square  miles,  though 
only  one  tenth  of  this  surface  appears  to  be  underlaid  by  productive  coal 
seams.  2.  The  second,  or  Great  Appalachian  coal  field,  extends  from  Penn- 
sylvania and  Ohio  to  near  Tuscaloosa,  in  the  interior  of  Alabama.  It  is 
about  875  miles  long,  and  is  estimated  to  contain  70,000  square  miles.  3.  A 
third,  and  smaller  coal  field,  occupies  the  center  of  the  State  of  Michigan ; 
it  covers  an  area  of  about  15,000  square  miles,  but  is  not  very  produc- 
tive. 4.  A  fourth  great  coal  field  is  situated  in  the  States  of  Kentucky,  Indi- 
ana, and  Illinois.  Its  area  is  estimated  at  50,000  square  miles.  5.  The 
fifth,  and  most  western,  occurs  in  Iowa,  Missouri,  and  Arkansas,  and  occu- 
pies an  area  of  about  57,000  square  miles.  Besides  these  great  deposits,  coal 
is  also  found  in  New  England,  Kansas,  Nebraska,  and  Texas. 

The  aggregate  space  underlaid  by  the  coal  fields  of  North  America  amounts 
to  at  least  200,000  square  miles,  or  to  more  than  twenty  times  the  area  which 
includes  all  the  known  coal  deposits  of  Europe. 

The  amount  of  coal  included  in  the  great  coal  fields  of  Europe  and  America 
has  been  approximately  estimated  by  Professor  H.  D.  Rogers,  as  follows  : 

Belgium, 36,000,000,000  tons. 

France,  59,000,000,000 

British  Islands,  190,000,000,000 

Pennsylvania,  -  316,400,000,000 

The  Great  Appalachian  coal  field,     -  -  1,357,500,000,000 

Indiana,  Illinois,  and  Kentucky,        -  -  1,277,500,000,000 

Iowa,  Missouri,  and  Arkansas,  -  739,000,000,000    " 

All  the  productive  coal  fields  of  North  America,     4,000,000,000,000     "* 

QUESTIONS. — What  is  said  of  the  yield  of  "mineral  oil"  springs  and  wells ?  What  is 
said  of  the  distribution  of  coal  in  the  Old  World?  What  of  the  coal  deposits  of  the 
United  States?  Where  are  the  great  coal  deposits  of  North  America  located? 


*  The  present  annual  product  of  the  chief  coal  producing  countries  is  nearly  as  follows  : 
Great  Britain,  80,000,000  tons;  the  United  States,  about  10,000,000;  Belgium,  about 
5,500,000 ;  France,  4,500,000.  The  total  annual  consumption  of  coal  in  the  world  Is  esti- 


248       FIRST     PRINCIPLES     OF     GEOLOGY. 

PERMIAN    SYSTEM. 

272.  This  system,  as  developed  in  Europe,  consists 
essentially  of  reddish  sandstones  and  conglomerates,  and 
of  common  and  magnesian  limestones,  with  deposits  of 
marls  and  gypsum.  It  derives  its  name  from  the  Govern- 
ment of  Perm,  in  Russia,  where  it  is  extensively  developed. 

It  was  formerly  supposed  that  the  Permian  system  was  not  represented  in 
North  America;  but  within  a  very  recent  period  deposits  of  this  age  have 
been  discovered  in  Illinois,  Kansas,  and  Nebraska.  Evidence  has  also  been 
adduced  by  Prof.  Emmons  showing  the  existence  of  Permian  strata  in  North 
Carolina;  and  the  same  geologist  supposes  that  a  portion  of  the  red  sand- 
stones of  the  Connecticut  River  Valley  and  of  the  Atlantic  slope  of  the  Ap- 
palachians also  belong  to  this  system. 

The  organic  remains  of  the  Permian  system  are  not  very  abundant,  and  do 
not  seem  to  differ  greatly  from  those  of  the  Carboniferous  system. 


273.  Close  of  the  Paleozoic  Period, — With  the  close  of  the 
Permian  system  the  Palaeozoic  period  terminates.  The  reason  for  drawing 
a  line  of  division  here  is,  that  there  occurred  about  this  time  a  vast  interval, 
during  which  the  part  of  the  world  now  occupied  by  "Western  Europe  (whence 
our  data  are  chiefly  derived)  seems  to  have  been  more  than  usually  affected 
by  forces  of  disturbance  and  destruction.  The  rocks  previously  deposited 
were  greatly  dislocated,  and  tilted  up  in  various  directions,  and  large  parts 
of  them  removed  by  the  action  of  water,  In  the  United  States,  the  great 
chain  of  the  Appalachian  Mountains,  which  stretch  from  New  England  to  the 
Southern  States,  is  supposed  to  have  been  elevated  at  about  this  epoch ;  since 
the  upper  strata  of  the  Carboniferous  system,  in  Pennsylvania,  are  greatly 
disturbed,  while  the  strata  of  later  ages,  which  cover  them,  have  not  been 
similarly  acted  upon.  Furthermore,  this  physical  break  and  discordance  in 
position  between  the  deposits  of  the  Paleozoic  and  those  of  subsequent  pe- 
riods was  accompanied  by  a  great  and  apparently  sudden  change  in  the  or- 
ganic remains  which  they  contain,  and  it  was  even  held  at  one  time  that  there 
was  not  a  single  organism — animal  or  vegetable — common  to  both  the  Palaeo- 
zoic and  Mesozoic  periods. 

QUESTIONS. — Where  is  the  Permian  system  principally  developed  ?  What  is  the  origin 
of  its  name?  Does  it  exist  in  this  country?  What  period  docs  the  Permian  system 
terminate?  Why  is  there  a  line  of  division  in  the  geological  series  drawn  here  ? 


mated  at  about  100,000,000  tons.  At  this  rate,  the  coal  fields  of  Pennsylvania  alone 
•would  meet  the  demand  for  3164  years ;  and  if  it  were  quadrupled— viz.,  400,000,000— 
the  productive  coal  fields  of  North  America  would  suffice  for  the  world's  supply  for 
10,000  years  to  come.  A  survey  of  these  figures,  therefore,  will  serve  to  dispel  any  ap- 
prehensions of  an  immediate  short  supply  of  coal ;  and  we  must  also  take  into  considera- 
tion that  new  coal  fields  are  discovered  as  geological  exploration  becomes  more  extensive 
and  exact. 


PERMIAN     SYSTEM.  249 

The  Palseozoic  period  was  characterized — 1st.  By  the 
non-existence,  so  far  as  is  yet  known,  of  birds,  or  of  any 
mammiferous  animals,  and  by  the  rarity  of  all  other 
vertebrate  animals,  except  fishes,  which  last  were  all 
distinguished  by  the  possession  of  unequally  lobed  or  he- 
terocercal  tails.  2d.  By  the  existence  of  many  peculiar 
types  and  genera  of  shells,  corals,  and  crinoids,  and  by 
large  numbers  of  trilobites,  of  which  we  find  no  trace 
afterward.  3d.  The  vegetation  that  flourished  upon  the 
earth  during  the  Paleeozoic  ages  was  remarkably  different 
from  that  of  subsequent  periods. 

There  was,  finally,  during  the  Palseozoic  age,  but  little  variety  among  the 
animals  of  the  different  regions  of  the  globe ;  and  this  may,  perhaps,  be  ex- 
plained by  the  peculiar  configuration  of  the  earth  at  that  period.  Greab 
mountains  did  not  then  exist ;  the  sea  covered  the  greater  part  of  the  sur- 
face of  the  globe ;  and  the  animals  which  then  existed  and  whose  remains 
have  been  preserved,  were  mostly  aquatic.  This  wide  distribution  of  the 
waters,  furthermore,  impressed  a  very  uniform  character  upon  the  whole 
animal  kingdom.  Between  the  different  zones  and  continents  no  such 
strange  contrasts  of  the  different  types  existed,  as  at  the  present  epoch. 
The  same  genera,  and  often  the  same  species,  were  found  in  the  seas  of 
every  quarter  of  the  globe ;  from  which  we  must  also  conclude  that  the 
climate  was  much  more  uniform  than  at  the  present  day. — AGASSIZ.* 

QUESTIONS. — What  were  the  principal  features  which  characterized  the  Palseozoic  age? 
What  is  said  of  the  uniformity  among  the  races  of  animals  that  prevailed  at  that  time  in 
different  parts  of  the  glohe? 


*  The  names  given  to  the  various  stratified  groups  of  rocks  included  in  the  Palseozoic 
period,  are,  as  has  already  been  remarked,  derived,  for  the  most  part,  from  the  geo- 
graphical districts  where  the  deposits  in  question  were  first  studied,  or  from  certain  narrow 
and  local  mineral  or  fossil  characteristics.  (See  §  185.)  As  the  study  of  geology,  how- 
ever, has  extended,  many  of  these  names  have  been  found  to  be  too  local  and  inexpressive, 
and,  in  fact,  often  inconsistent  with  the  real  characters  of  the  formations,  as  determined 
by  later  investigations.  To  avoid  these  difficulties,  therefore,  Prof.  H.  D.  Rogers  has 
proposed  to  divide  the  American  geological  formations,  extending  from  the  lowest  de- 
posited in  the  dawn  of  organic  life  to  these  formed  at  the  end  of  the  Coal  period  (accord- 
ing to  certain  -well-marked  fossil  or  physical  peculiarities),  into  fifteen  groups  or  series  of 
deposits,  and  to  designate  them  by  names  significant  of  their  relative  ages.  To  accom- 
plish this,  he  employs  words  which  suggest,  metaphorically,  the  different  natural  pe- 
riods of  the  day;  and  which,  commencing  with  the  lowest  of  the  series,  are  as  follows:— 
Primal,  Auroral,  Matinal,  Levant,  Surgent,  Scalent,  Pre-mcridian,  Meridian,  Post- 
meridian, Cadent,  Vergent,  Ponent,  Vespertine,  Umbral,  and  Serai — meaning,  respect- 
ively, the  formations  of  the  Dawn,  Daybreak,  Morning,  Sunrise,  Mounting  Day,  Climb- 
ing Day,  Forenoon,  Noon,  Afternoon,  Declining  Day,  Sunset,  Evening,  Dusk,  and  Night- 
fall.  Such  a  nomenclature  of  the  Palseozoic  formations,  based  on  time,  is  desirable :  and, 
though  not  at  present  adopted  to  any  great  extent,  it  may  be,  ultimately. 

11*    . 


250       FIRST     PRINCIPLES     OF     GEOLOGY. 


MESOZOIC  PERIOD. 

274.  The  stratified  rocks  of   the  Mesozoic  '(i.  e.,  the 
middle  period  of  geological  time)  are  arranged  into  three 
systems,  viz.  :    the  Triassic  (sometimes  called  the  New 
Red  Sandstone),  the  Oolitic  or  Jurassic,  and  the  Creta- 
ceous. 

TRIASSIC    SYSTE  M.—New  Red  Sandstone. 

275.  This  system  derives  its  name  Trias  (triple  series) 
from  the  circumstance  that  it  is  composed,  in  continental 
Europe — where  it  is  very  fully  developed, — of  three  dis- 
tinct groups  of  sandstones,  limestones,  and  marls. 

In  England,  the  rocks  of  this  system  are  principally  red  sandstones  and  red 
marls ;  and  hence  the  early  English  geologists  gave  to  them,  collectively,  the 
name  of  "New  Red  Sandstone"  in  contradistinction  to  the  "  Old  Red  Sand- 
stone" (Devonian),  which  lies  below  the  Carboniferous  system.  As  this  sys- 
tem is  also  noted,  in  Europe,  for  containing  large  .deposits  of  rock-salt,  it  is 
sometimes  termed,  moreover,  the  "Saliferous"  (salt-bearing)  system. 

Distribution, — In  the  United  States,  the  Triassic  system  is  probably 
represented  by  a  part  of  the  shales  and  sandstones  found  in  the  Valley  of 
the  Connecticut  River,  and  also  in  Eastern  New  Jersey,  Yirginia,  and  North 
Carolina.  Deposits  referable  to  this  age  are  also  believed  to  exist  in  the 
territory  of  Utah  and  New  Mexico. 

Life  of  the  Epoch, — The  red  sandstones,  marls,  and  shales,  which 
constitute  a  large  proportion  of  the  rocks  of  this  system,  are  very  barren  of 
fossils;  and  it  may  be  here  remarked,  that,  as  a  general  rule,  fossils  are 
always  more  rare  in  red  rooks  than  in  those  of  any  other  color.  The  matter 
imparting  the  red  color  (peroxyd  of  iron,  etc.)  seems  to  have  been  either 
destructive  of  life  in  the  seas  in  which  it  prevailed,  or  else  it  was  ill  adapted 
to  the  preservation  of  the  remains  of  animals  that  were  deposited  along  with 
it.  In  the  limestones  and  other  rocks  of  this  system,  devoid  of  a  red  color, 
fossils  are,  however,  often  very  abundant. 

As  has  been  already  stated,  the  Triassic  system — forming  the  commence- 

QTJESTIONS.— What  system  constitutes  the  base  of  the  rocks  referred  to  the  Mesozoic 
period?  What  is  the  origin  of  the  name  "  Trias?"  By  what  other  names  has  this  sys- 
tem been  designated  ?  What  is  said  of  its  distribution  in  the  United  States  ?  "Where  is 
it  most  fully  developed  ?  What  is  said  of  the  life  of  this  period  ?  What  class  of  rocks 
are  characteristically  barren  of  fossils? 


TRIASSIC      SYSTEM.  251 

ment  of  the  Mesozoic  period — is  considered  as  marking  the  dawn  of  a  new 
circle  of  organic  life  upon  the  surface  of  our  planet.  "  In  passing  upwards," 
says  Hugh  Miller,  "  from  the  Permian  to  the  Triassic,  we  seem  to  pass  not 
merely  from  one  dynasty  to  another,  but,  if  I  may  employ  such  a  term,  from 
one  dispensation  to  another."  The  singular  and  typical  plants  of  the  Carboni- 
ferous system — the  lepidodendra,  the  sigillaria,  and  the  like — have  nearly  all 
disappeared,  and  given  place  to  forms  more  nearly  allied  to  the  tropical 
plants  of  the  present  day.  "We  find,  moreover,  in  the  Triassic  rocks,  none 
of  the  curious  corals  of  the  Silurian,  Devonian,  and  Carboniferous  sys- 
tems, comparatively  few  crinoids,  no  trilobites,  no  strange-looking,  bone- 
encased  fishes;  and  now,  for  the  first  time,  we  find  fishes  with  homocercal, 
or  equally  lobed  tails,  while  the  heterocercal,  or  unequally  lobed  form,  ceased 
to  be  the  universal  or  common  characteristic  of  this  class  of  animals. 

In  the  rocks  of  the  Palaeozoic  period  the  remains  of  only  a  few  reptiles 
have  been  discovered,  and  it  is  not  probable  that  this  class  of  animals  had, 
at  this  age  of  the  world,  any  great  development.  During  the  Triassic  epoch, 
however,  we  have  evidence  that  reptiles  existed  in  large  numbers,  and  of 
the  most  peculiar  characters. 

FIG.  160. 


One  of  the  most  remarkable  of  these  was  the  "  Labyrinthodon,"  a  strangely 
formed  reptile,  unlike  anything  which  now  exists.  It  more  resembled  a 
frog  or  toad  than  any  animal  with  which  we  are  now  acquainted ;  but,  in 
addition  to  its  frog-like  peculiarities,  it  had  the  head  and  teeth  of  a  crocodile, 
and  a  size  but  little  inferior  to  that  of  an  ox.  The  prints  of  its  feet,  which 
are  impressed  and  preserved  on  the  surfaces  of  the  Triassic  sandstones,  as 
clearly  as  if  the  animal  had  traversed  the  muddy  beach  of  yesterday,  very 
much  resemble  those  of  the  human  hand ;  but,  as  in  the  frog,  the  hinder 
paws  were  fully  twice  the  size  of  the  fore  ones.  Fig.  160  represents  a  re- 
stored outline  of  this  animal,  and  the  appearance  of  its  tracks. 

In  the  uppermost  beds  of  the  triassic  system  we  obtain 
the  first  vestiges  of  the  existence,  upon  the  earth,  of  warm- 

QUESTIONB.— In  what  respect  is  the  Triassic  system  particularly  distinguished  from 
the  systems  that  preceded  it?  What  class  of  animals  were  especially  developed  during 
this  age  ?  What  remarkable  reptile  then  existed? 


252       FIRST     PRINCIPLES     OF     GEOLOGY. 

blooded,  air-breathing,  vertebrate  animals,  viz.,  the  teeth 
and  vertebree  of  several  species  of  small  quadrupeds. 

These,  from  the  structure  of  their  bones,  it  is  inferred,  must  have  belonged 
to  the  order  of  marsupalia  (pouched  animals) — the  lowest  group  of  the  sub- 
kingdom,  Mammalia.0  The  most  ancient,  probably,  of  these  remains  have 
been  found  by  Prof.  Emmons,  in  North  Carolina. 

It  may  here  be  observed,  that  although  no  specimens  of  so  large  a  class  of 
animals  as  mammalia  are  found  earlier,  yet  such  may,  nevertheless,  have 
existed,  and  the  defect  may  be  in  our  not  having  found  them ;  but  other 
things  considered,  the  probability  is  that  heretofore  none  existed.  It  is  also 
an  interesting  circumstance,  that  the  first  mammals  found  should  have  be- 
longed to  the  mursupialia,  when  the  place  of  that  order  in  the  scale  of  crea- 
tion is  considered. 


OOLITIC,    OR    JURASSIC    SYSTEM. 

276.  This  system  is  sometimes  termed  the  Oolitic,  from 
the  oolitic  texture  of  many  of  the  limestones  that  belong 
to  it  (see  §  15);  and  sometimes  the  Jurassic,  from  the 
circumstance  that  it  is  extensively  developed  among  the 
Jura  Mountains  of  Switzerland. 

277.  Distribution, — The  Oolitic  system  is  typically  more  developed,' 
and  has  been  more  minutely  studied,  in  England,  than  in  any  other  portion 
of  the  globe;  and  it  there  consists  of.  three  well-marked  groups  of  strata — 
the  "Lias,"f  occupying  the  lowest  portion  of  the  system;  the  "  Oolite,"  the 
middle  portion;  and  the  ""Wealden"  the  upper.:}:    In  France,  Switzerland,  and 


QUESTIONS. — What  is  said  of  the  existence  of  -warm-blooded  animals  at  this  epoch  ? 
What  system  succeeds  the  Trias  in  the  ascending  order  of  the  series?  Give  the  de- 
rivation of  the  names  applied  to  it  ?  Where  is  the  Oolitic  system  most  extensively  de- 
vcloped  ? 


*  By  marsupial  quadrupeds  arc  understood  those  animals  -which  possess  a  pouch  in 
•which  the  prematurely-born  young  are  nursed  and  carried  about  by  the  mother  until 
able  to  take  care  of  themselves.  Of  these  creatures  the  kangaroo  is  the  best  known,  and 
largest  representative  at  present  existing.  The  opossum  is  the  only  representative  of  this 
group  found  in  North  America.  All  these  animals  are  nocturnal  in  their  habits,  so  that 
it  rarely  happens  that  the  traveler  discovers  their  existence,  even  in  districts  in  which  the 
smaller  kinds  may  be  comparatively  abundant. 

t  This  tenri  is  said  to  be  a  corruption  of  the  word  "  Z&rs,"  or  "  layers,"'  and  was  origin- 
ally applied  to  the  thin  beds,  -which  characterize  the  limestones  occuring  at  the  base  of 
the  Oolitic  system. 

$  So  distinct  in  many  respects  are  the  groups  of  the  Lias  and  Oolite,  that  they  are  some- 
times treated  as  independent  systems  ;  and  it  is  not  improbable  that  the  progress  of  dis- 
covery -will  ere  long  compel  geologists  to  adopt  this  arrangement  universally. 


OR     JURASSIC     SYSTEM.  253 

Germany,  the  system  is  also  largely  developed ;  but  in  these  countries  the 
deposits  are  mainly  referred  to  the  groups  of  the  Lias  and  the  Oolite ;  the 
Oolite  also  occurs  on  a  large  scale  in  India. 

In  the  United  States  the  Oolitic  or  Jurassic  system  occupies,  comparatively, 
but  a  very  small  area.  The  upper  portion  of  the  series  of  shales  and  sand- 
stones found  in  the  Connecticut  Eiver  Valley,  and  in  New  Jersey,  are  now 
generally  believed  to  belong  to  this  age,  as  is  also  a  deposit  of  sandstones, 
containing  workable  beds  of  coal,  near  Richmond,  Va. 

Numerous  fossils,  peculiar  to  this  system,  have  also  been  recently  brought  by 
the  expeditions  in  search  of  Sir  John  Franklin,  from  extreme  Arctic  regions. 

218.  Characteristics  of  the  Oolitic  System. — This  system  is 
mainly  composed  of  limestones,  calcareous  sandstones,  clays,  shales,  and  oc- 
casionally seams  of  coal.*  There  is  no  particular  appearance  of  disturbance, 
so  far  as  has  been  observed,  in  Europe,  between  the  strata  which  mark  the 
close  of  the  Triassic  system  and  the  beginning  of  the  Oolitic ;  but  there  is,  in 
Europe,  a  noticeable  change  in  the  constituent  materials  of  the  rocks  of  the 
two  systems  (i.  e.,  from  sand  to  lime) ;  thus  indicating,  that  while  the  bottoms 
of  the  seas  of  one  epoch  were  chiefly  arenaceous  (sandy),  those  of  the  latter 
were  chiefly  limey  and  clayey. 

279.  Life   of  the   Epoch  , — The  organic  remains  of  the  Ooh'tic  system 
are  all  Mesozoic — that  is,  they  belong  to  genera  and  species  differing  from 
those  found  in  the  Paleozoic  rocks,  and  differing  also,  though  less  in  general 
aspect,  from  those  found  in  the  rocks  of  the  Cainozoic  or  subsequent  period. 
They  are  exceedingly  numerous  and  well  preserved — particularly  in  the  de- 
partment of  animals — and  more  particularly  still,  in  the  class  of  molluscs, 
which,  it  has  been  observed,  are  always  more  conspicuous  in  a  system  in 
proportion  to  the  predominance  in  it  of  calcareous  rocks. 

In  this  system,  we  likewise  find  that  same  uniformity  over  great  space  which 
has  been  remarked  of  the  fossils  of  the  earlier  systems.  In  the  Oolitic  rocks 
of  the  Himalaya  Mountains,  of  South  America,  of  the  region  north  of  the 
Cape  of  Good  Hope,  and  in  India,  fossils  have  been  found,  which,  as  far  as 
naturalists  can  determine,  are  undistinguishable  from  fossils  occurring  in  the 
Oolite  and  Lias  of  Europe. 

280.  Vegetation,— The  vegetation  of  the  Oolitic  era  was 
extremely  varied,  but  the  highest  order  of  plants  which 

QUESTIONS.— What  is  said  of  its  occurrence  in  the  United  States?  What  is  the  charac- 
ter of  the  rocks  composing  the  Oolitic  system  ?  In  what  respect  do  they  particularly  differ 
from  the  rocks  of  the  Triassic  system  ?  What  is  said  of  the  life  of  this  epoch  ? 


*  The  light-colored  "  Caen  Stone,"  which  has  been  of  late  years  extensively  imported 
into  this  country  from  the  north  of  France,  and  examples  of  which  may  be  seen  in  build, 
ings  in  New  York  City  (i.  e.^  the  Nassau  Bank),  and  in  the  interior  construction  of  many 
churches,  is  a  sandstone  of  this  system.  So  are  also  the  fine-grained,  cream-colored 
limestones  imported  from  Germany  for  "  lithographic  stones." 


254        FIRST     PRINCIPLES      OF      GEOLOGY. 


then  existed  appear  to  have  been  coniferous  (cone-bear- 
ing) ;  "  and  as  yet  no  example  of  a  true  exogenous  timber 
tree  has  been  detected/' 

Among  the  most  characteristic  forms  of  this  age  was  a  beautiful  family  of 
plants,  intermediate  in  character  between  palms,  pines,  and  ferns,  termed 
Cycadacese  (single  plant,  Cycas),  some  of  which  had  short,  cylindrical,  scaly 
stems,  surmounted  by  a  tuft  of  elegant  leaves,  resembling  a  pine-apple  ;  while 
others  had  tall,  straight  trunks  twenty  or  thirty  feet  in  height.  The  struc- 
ture of  the  cycas  is  shown  at  3,  Fig.  161,  which  represents  a  restored  aspect 
of  the  Oolitic  vegetation.  There  were  also  tree  ferns  (see  Fig.  161,  No.  2), 
but  in  smaller  proportion  than  in  former  ages,  palms  (1  and  4),  pines  (5),  and 
numerous  plants  resembling  the  aloe,  the  agave,  pine-apple,  etc.  (6,  7,  and  8). 

FIG.  161. 


The  vegetation,  in  short,  of  the  Oolite,  was  generally  analogous  to  that 
which  now  prevails  at  the  Cape  of  Good  Hope,  and  in  some  of  the  Islands  of 
the  Pacific;  and  seems  to  indicate  a  climate  (apparently  a  universal  climate) 
between  the  tropical  and  the  temperate.  It  was  also  sufficiently  luxuriant 
to  produce  deposits  of  coal,  which  are  sometimes  workable.  One  of  the  most 
remarkable  of  these  occurs  near  Richmond,  in  Virginia ;.  and,  although  the 
coal  in  this  locality  has  been  derived  from  an  assemblage  of  plants,  very  dis- 
tinct specifically  and  in  part  generically,  from  those  which  contributed  to  the 
formation  of  the  more  ancient  or  Pakeozoic  coal,  yet"  it  is  not  surpassed  in 

QUESTIONS.— "What  is  said  of  the  vegetation  of  the  Oolite?  What  were  some  of  the 
most  characteristic  forms  of  this  age  ?  What  is  said  of  the  existence  of  coal  in  this  sys- 
tem ?  Where  does  the  most  remarkable  deposit  of  Oolitic  coal  occur  ? 


OOLITIC,    OR     JURASSIC     SYSTEM.  255 


quality,  and  is  abundant  in  quantity — the  main  seam  in  some  places  being 
from  thirty  to  forty  feet  thick,  and  composed  of  pure  bituminous  coal.* 

Lignite  , — Most  of  the  deposits,  however,  of  vegetable  matter,  found  in 
the  Oolitic  system,  and  in  all  the  other  geological  systems  also  more  recent 
than  the  Carboniferous,  have  not  experienced  a  sufficient  deg&e  of  mineral- 
ization to  convert  them  into  true  coal ;  but  they  form  an  imperfect  variety 
of  coal,  termed  Lignite  (Lat,  lignum,  wood),  or  Brown  Coal,  which,  in  general, 
resembles  charcoal,  and  exhibits  the  ligneous  texture  of  the  wood  more  or 

less  distinctly. 

FIG.  162. 


Limestones 


Dirt-bed, 

with  stumps 

of  trees. 


Limestones. 


, . 


One  of  the  most  interesting  facts  connected  with  the  vegetation  of  the 
Oolitic  period,  is  the  occurrence,  in  certain  localities  in  England — interstrati- 

QTTESTIONS. — In  what  condition  do  deposits  of  vegetable  matter  generally  occur  in  the 
systems  more  recent  than  the  Carboniferous  ?    What  is  lignite  ? 


*  The  whole  productive  area  of  this  Oolitic  Virginia  coal-field  has  been  estimated  at 
about  185  square  miles,  or  about  twenty-six  miles  in  length,  and  from  four  to  twelve  in 
breadth.  "  The  coal  occurs  at  the  base  of  a  series  of  quartzose  sandstones,  and  shales, 
and  reposes  almost  directly  upon  granite.  The  whole  of  the  central  area  is  covered  by 
conglomerates."  Fig.  163  represents  a  section  of  this  Eastern  Virginia  coal  field,  show- 
ing the  inclined  position  of  the  coal  seams,  and  the  manner  in  which  the  pits  or  shafts 
have  been  sunk  to  reach  them. 

FIG.  163. 


II 

P? 


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a 

5? 

O    tO 

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^ 

o  ^ 

o 

C3l 

1* 

p 

P 

3  £ 

• 

* 

• 

^3    f^ 

T? 

^^>^mi[ 

"^tnr  — 

:                        Conglomerate. 

-T 

^^\ 


Granite. 


Deep  "Working?, 
880  f(t.  deep. 


Granite. 


256 


FIRST     PRINCIPLES     OF     GEOLOGY. 


fied  with  limestones  and  sandstones, — of  dark  loam-like  strata,  locally  known 
as  "dirt-beds,"  which  appear,  from  incontestable  evidence,  to  have  been  the 
soils  on  which  grew  the  Cycadacese  and  other  plants  of  this  era.  In  one 
locality  at  the  Isle  of  Portland,  on  the  coast  of  England,  we  find,  Bays  Mr. 
Bake  well,  "within  a  distance  of  two  feet,  an  entire  change,  from  strata  con- 
taining marine  shells,  to  strata  once  supporting  terrestrial  plants  ;  and, 
should  any  doubt  arise  respecting  the  original  place  and  condition  of  these 
plants,  there  is  over  the  lower  dirt-bed  a  stratum  of  limestone  containing 
fresh-water  shells,  and  upon  this,  a  thick  dirt-bed,  in  which  are  stumps  of 
trees,  from  three  to  seven  feet  in  height,  mostly  erect,  with  their  roots  ex- 
tending beneath  them.  Trunks  of  trees  are  also  found  embedded  in  the 
same  stratum,  some  of  which  are  from  twenty  to  twenty-five  feet  in  length, 
and  from  one  to  two  feet  in  diameter."  A  section  of  the  strata  at  this  local- 
ity is  represented  in  Fig.  162.  Fig.  32,  page  75,  represents  one  of  these  dirt- 
beds  included  between  inclined  strata. 

281.  Animals, — The  animal  remains  found  in  the  Oolitic 
or  Jurassic  system  represent  almost  every  existing  order, 
with  the  exception  of  the  higher  mammalia — thus  ex- 
emplifying the  fact  that  there  was,  during  all  the  geologi- 
cal ages,  a  constant  and  upward  progress  in  creation — but 
leaving  us  in  ignorance  of  the  means  by  which  the  creative 
power  accomplished  its  designs. 

FIG.  164. 


The  invertebrate  inhabitants  of  the  oceans  of  the  Oolito— the  corals, 
sponges,  star-fishes,  crinoids,  and  molluscs — were  extremely  abundant.  Of 
the  molluscs,  the  class  of  cephalopods  (swimming  shell-fish)— creatures  of 
high  standing  in  their  department  of  the  Animal  Kingdom,  and  represented 


QUESTIONS.— What  interesting  fact  has  been  brought  to  light  respecting  the  vegetation 
of  the  Oolite  ?  What  is  said  of  the  animal  remains  found  in  the  Oolite  ?  What  two 
genera  of  molluscs  •were  especially  abundant  ? 


OOLITIC,     OR     JURASSIC     SYSTEM.         257 


FIG.  166. 


at  the  present  day  by  the  nautilus  and  the  cuttle-fish — existed  in  vast  num- 
bers ;  greater,  in  fact,  at  this  period  of  the  world's  history  than  in  any  former, 
or  at  any  subsequent  time. 

Two  genera,  however,  were  so  remarkable  and  abundant,  that  they  may  be 
almost  said  to  characterize,  of  themselves,  the  rocks  of  the  Oolite,  viz. :  The 
Ammonites  and  the  Belemnites.  The  former  had  essentially  the  same  cham- 
bered structure  as  the  Orthoceratites  (see  §  240),  but  instead  of  being  straight, 
like  them,  they  were  coiled  up  in  a  plane  spiral.  (See  Figs.  164  and  165,  which 
represent  two  species  of  Ammonites.)  The  range  of  this  genus  is  from  the 
Triassic  to  the  Cretaceous  systems,  including  the  Oolite, 
where,  as  already  said,  it  attains  its  greatest  develop- 
ment ;  and  from  the  strata  of  these  systems  more  than 
500  distinct  species  have  been  described — the  sheila 
varying  in  size  from  a  half  an  inch  to  three  feet  in  diam- 
eter. At  the  close  of  the  Mesozoic  period  the  genus  be- 
came extinct,  and  at  present  there  are  no  similar  shells 
living. 

282.  The  Belemnite  (Gr.,  flel.e/Livov,  a  dart)  is  a  cylin- 
drical shell,  terminating  at  one  extremity  in  a  point, 
and  having  at  the  opposite,  or  largest  end,  a  conical 
cavity.  (See  2,  Fig.  166.)  Some  specimens  are  several 
inches  in  circumference,  and  from  ten  to  twelve  inches 
in  length.  They  are  found  in  great  numbers  in  the 
rocks  of  the  Oolitic  and  Cretaceous  systems ;  and  on 
the  continent  of  Europe  there  are  limestones  which  are 
almost  wholly  composed  of  them.  For  a  long  time  it 
was  a  question  with  geologists,  what  was  the  nature 
of  the  animal  to  which  this  singular  shell  belonged, 
but  it  is  now  known  to  have  been  the  internal  bone  of  an  extinct  cephalo- 
pod,  allied  to  the  squid  or  the  cuttle-fish  of  our  day.  Fig.  1 66,  Xo.  1,  shows 
the  restored  appearance  of  the  animal,  and  a  the  position  of  the  belemnite. 
This  creature  was  furnished  with  an  ink-bag  (like  the  existing  cuttle-fish, 
which  furnishes  the  material  for  the  preparation  of  the  dark  pigment  known 
as  sepia),  with  which  it  could  muddle  the  water  around  it,  and  thus  protect 
itself  against  the  attack  of  more  powerful  animals.  In  some  instances  these 
ink-bags — more  than  a  foot  in  length — have  been  found  attached  to  the  be- 
lemnite, with  the  ink  material  in  them  so  well  preserved  that  it  has  actually 
been  employed  as  a  pigment.* 

QUESTIONS. — Describe  the  structure  of  the  Ammonites?     Describe  the  Belemnitea? 
What  is  said  of  the  fishes  of  the  Oolite  ? 


*  Some  idea  of  the  richness  of  the  rocks  of  this  system  in  marine  fossils  may  be  gained 
from  the  following  description  of  a  portion  of  the  lias  of  Scotland,  by  Hugh  Miller:  "It 
consists  of  laminaj  as  thin  as  sheets  of  pasteboard,  -which,  of  course,  shows  that  there  was 
but  little  deposited  at  a  time,  and  pauses  between  each  deposit.  Yet  never  did  characters 
or  figures  lie  closer  on  a  printed  page,  than  the  organisms  on  the  surfaces  of  these  leaf-liko 
laminae.  We  insinuate  our  lever  into  a  fissure,  and  turn  up  a  portion  of  one  of  the 


258       FIRST     PRINCIPLES     OF     GEOLOGY. 

283.  Fishes  , — In  many  of  the  strata  of  tho  Oolitic  system,  the  remains 
of  fish — placoids  and  ganoids — are  abundant.  The  forms  are,  however,  with 
few  exceptions,  different  from  those  found  in  the  strata  of  any  of  the  preced- 
ing systems. 

284.  Reptiles, — But  the  most  striking  circumstance 
connected  with  the  life  of  this  epoch,  was  a  most  re- 
markable development  of  reptilian  forms  of  life,  which 
existed  in  such  numbers  that  the  Mesozoic  period  of  our 
earth's  history  is  often  spoken  of  as  the  "Age  of  Reptiles." 

Some  of  the  most  remarkable  of  these  reptiles  are  known  among  geologists 
and  naturalists  under  the  generic  names  of  Ichthyosaurus,  Plesiosaurus,  Me- 
gatosaurus,  Iguanodon,  Pterodactyle,  etc. 

FlG.  167. 


The  Ichthyosaurus  (Gr.,  fish-lizard}  -was  a  sort  of  reptile- whale, 
that  attained,  in  some  instances,  a  length  of  thirty  feet  or  upwards.  Its 
general  bodily  form  was  that  of  a  fish,  to  which  was  added  the  head  and 

QUESTIONS.— What  class  of  animals  -was  especially  developed  during  this  epoch  ?  What 
name  is  sometimes  given  to  the  Mesozoic  period  ?  What  -were  some  of  the  more  remark- 
able reptiles  ?  Describe  the  Ichthyosaurus. 


laminae,  whose  surface  had  last  seen  the  light  when  existing  as  part  of  the  bottom  of  the 
old  Liassic  sea,  when  more  than  half  of  the  formation  had  still  to  be  deposited.  Is  it  not 
one  of  the  parts  of  Sowerby's  "Mineral  Conchology"  that  has  opened  up  to  us?  Nay, 
the  shells  lay  too  thickly  for  that,  and  there  are  too  many  repetitions  of  the  same  species. 
The  ground  of  the  tablet  is  of  a  deep  black,  while  the  colors  of  the  fossils  stand  out  in 
various  shades,  from  opaque  to  a  silvery  white  or  deep  gray.  There,  for  instance,  is  a 
group  of  large  ammonites,  as  if  drawn  in  white  chalk ;  there,  a  cluster  of  minute  bivalve 
shells,  each  of  which  bears  its  thin  film  of  silvery  nacre.  We  turn  over  another  page. 
It  is  occupied  extensively  by  ammonites  of  various  sizes,  but  all  of  one  species,  as  if  a 
whole  argosy,  old  and  young,  convoycs  and  convoyed,  had  been  wrecked  at  once,  and 
sent,  disabled  and  dead,  to  the  bottom.  "And  here  we  open  yet  another  page  more.  It 
bears  a  set  of  extremely  slender  belemnites.  They  lie  along,  and  athwart,  and  in  every 
possible  angle,  like  a  heap  of  boarding-pikes  thrown  carelessly  down  a  vessel's  deck  on 
the  surrender  of  the  crew.  Here,  too,  is  an  assemblage  of  bright,  black  plates,  that  shine 
like  pieces  of  Japan  work— the  head-plates  of  some  fish  of  the  ganoid  order ;  and  here 
an  immense  accumulation  of  minute,  glittering  scales  of  a  circular  form.  We  apply  the 
microscope,  and  find  every  little  interstice  in  the  page  covered  with  organisms.  And 
leaf  after  leaf,  for  tens  and  hundreds  of  feet  together,  repeats  the  same  strange  story. 
The  great  Alexandrian  library,  with  its  unsummed  tomes  of  ancient  literature,  the  ac- 
cumulation of  long  ages,  was  but  a  poor  and  meagre  collection,  scarce  less  puny  in  bulk 
than  recent  in  date,  when  compared  with  this  vast  and  wondrous  library  of  the  lias  of 
Scotland." 


OOLITIC,     OR     JURASSI<3     SYSTEM.          259 


breast-bone  of  a  lizard ;  the  paddles  of  a  whale ;  the  snout  of  a  porpoise, 
and  the  teeth  of  a  crocodile.    Its  structure  is  represented  in  Fig.  167. 

The  Ichthyosaurus,  however,  was  a  true  air-breathing  animal,  and  could 
do  what  no  whale  or  porpoise  of  the  present  day  is  capable  of  accomplishing, 
viz.,  it  could  crawl  upon  the  shore  as  do  the  seals  and  the  walrus.  It  had 
an  enormous  eyeball,  which  was  larger,  in  proportion  to  the  skull,  then  the 
eye  of  any  other  animal — the  orbital  cavity  in  one  species  being  fourteen 
inches  in  its  longest  diameter;  and  this  eye,  having  no  eye-lids,  was  pro- 
tected from  injury  by  a  casing  of  numerous  thin,  and,  probably,  flexible 
bones.  (See  Fig.  168.)  The  length  of  its  jaws  was  sometimes  upward  of  six 
feet,  and  its  teeth  were  numerous  and  formidable.  (See  Fig.  168.) 

FIG.  168. 


The  skin  of  the  Ichthyosaurus  (some  portions  of  which  have  been  found  fossil) 
was  naked,  like  that  of  the  whale,  and  not  covered  with  scales.  Owl-like,  it 
probably  pursued  its  prey  at  night,  and  must  have  been  exceedingly  destruc- 
tive to  the  animals  with  which  it  was  associated.  In  some  instances,  the 
petrified  stomach  of  the  Ichthyosaurus  has  been  found  in  connection  with  its 
skeleton,  filled  with  the  half-digested  fossilized  remains  of  fish,  other  reptiles, 
and  even  with  the  young  of  its  own  species. . 


FIG.  169 


The  Plesiosaurus  (Gr.,  Trfycioc,  near  to ;  •  and  aavpoc,  a  lizard)  was 
another  marine  reptile,  ranging  from  ten  to  twenty  feet  in  length,  which  has 
been  likened  to  "a  turtle  threaded  through  with  the  body  of  a  snake."  (See 
Fig.  169.  Its  head,  which  resembled  a  lizard's,  was  very  small ;  its  paddles 


260      FIRST     PRINCIPLES     OF     GEOLOGY. 


were  large,  and  like  those  of  a  turtle ;  and  its  tail  was  like  that  of  a  croco- 
dile. But  the  most  remarkable  feature  about  this  animal  was  the  enormous 
length  of  its  neck.  Thus,  while  the  mammalia  have  not  generally  more  than 
five  cervical  (neck)  vertebra,  and  birds  from  nine  to  twenty-four  (the  swan), 
the  Plesiosaurus  had  from  twenty  to  forty. 

This  reptile  was  carnivorous  ;  but  unlike  the  Ichthyosaurus,  which  was  a 
deep-sea  animal,  it  was  probably  a  shore  creature,  and  lived  in  bays  and 
shallow  waters;  and  there,  "lurking  under  marine  vegetation,  obtained  its 
prey  by  darting  out  its  long  neck,  and  seizing  it  with  its  sharp  and  formida- 
ble teeth." 

FIG.  170. 


Crocodiles  of  various  species,  and  often  of  great  size,  were  contemporary  in- 
habitants of  the  same  seas  as  the  Icthyosaurus  and  Plesiosaurus.  Fig.  170 
represents  the  fossil  head  and  jaws  of  one  species.  "We  also  find,  in  the 
rocks  of  this  epoch,  the  bones  and  the  tracks  of  chelonians  or  tortoises,  and 
hi  some  instances,  what  appear  to  have  been  the  eggs  of  these  animals  (clus- 
tered together  as  originally  deposited  in  the  sands  of  the  ancient  Oolitic  sea- 
shore), have  been  found  fossil. 

285.  Coprolites  • — In  connection  with  the  remains  of  fishes  in  the  Car- 
boniferous system,  and  with  the  remains  of  fishes  and  marine  reptiles  in  the 
FIG.  171.  rocks  of  the  Mesozoic  period,  there  are 

found  certain  curious  organic  bodies, 
which  all  geologists  are  agreed  are 
the  fossilized  "  voidings"  or  a  excre- 
ments" of  the  above  referred  to  ani- 
mals ;  and  which  have  received  the 
name  of  Coprolites  (Gr.,  Ko-rrpoc,  dung  ; 
and  /U00f,  a  stone).  These  Copro- 
lites, iii  many  instances,  contain 
scales,  fragments  of  shells,  bones,  etc, 
— the  undigested  portions  of  the  ani- 
mals on  which  the  carniverous  fish  or 
reptiles  preyed — and  often  exhibit  on 
their  surfaces  the  corrugation  and 
vascular  impressions  of  the  intes- 
tines. (See  Fig.  171.)  In  the  rocks  of  the  Oolitic  and  Cretaceous  systems, 
Coprolites  are  especially  abundant,  so  much  so,  that  at  certain  localities  in 
England  (which,  says  Mr.  Buckland,  would  seem  to  have  been  cloaca  maxima 
of  the  ancient  ocean)  they  constitute  a  notable  proportion  of  the  strata;  and, 


QUESTION.— Describe  the  marine  reptiles  of  the  Oolite. 


OR     JURASSIC     SYSTEM.          261 

on  account  of  the  large  percentage  of  phosphate  of  lime  contained  in  them, 
are  regularly  quarried,  pulverized,  and  used  as  manure.* 

286.  Land  Animals  of  the  Oolite, — But  remarkable  as  were  the 
inhabitants  of  the  Oolitic  ocean,  the  dry  land  of  this  epoch  must  have  ex- 
hibited forms  far  more  monstrous  and  gigantic.  The  most  noticeable  of  these 
•were  the  so-called  " Megalosaurus,"  "  Hyfaosaurus,"  and  "  Iguanodon,"  all  of 
which  were  enormous  terrestrial  "  crocodile  lizards,"  or  saurians,  covered  with 
scales. 

The  Megalosaurus  -was  about  thirty  feet  in  length,  and,  judging  from  the 
sharp,  trenchant  teeth  that  still  remain  implanted  in  its  fossil  jaws,  was  a 
highly  carnivorous  and  ferocious  animal,  devouring,  in  all  likelihood,  smaller 
reptiles,  and  the  young  of  its  gigantic  contemporaries. 

The  HylcBosaurus  was  a  smaller  reptile,  of  from  twenty  to  twenty-five  feet  in 
length,  which  had  a  row  of  very  large,  thin  angular  spines,  extending  like  a 
serrated  fringe  along  its  back.  An  existing  tropical  lizard,  the  cyclura  (see  Fig. 
172),  has  been  supposed  somewhat  to  resemble  the  Hylseosaurus  in  miniature. 

FIG.  172. 


The  Iguanodon  is  proved,  by  the  form  of  its  teeth  and  by  the  partially 
digested  vegetable  matter  (portions  of  coniferous  and  cycadaceous  plants) 
found  in  connection  with  its  skeleton,  to  have  been  an  herbivorous  (plant- 
eating)  reptile ;  and  in  structure  and  habits  probably  resembled  the  Iguana 
(lizard)  of  the  TVest  Indies,  from  whence  it  derives  its  name.  In  size,  it 
rivaled  the  largest  elephant  in  height,  and  greatly  more  than  rivaled  him  in 
length  and  bulk — its  average  length  being  about  thirty  feet,  though  some 
specimens  are  supposed  to  have  attained  a  length  of  from  sixty  to  seventy 
feet.  The  limbs  of  the  Iguanodon  must  have  been  of  proportionate  size  arid 
strength  to  sustain  and  move  so  enormous  a  carcass.  The  hinder  extremi- 

QUESTIONS. — What  was  the  character  of  the  land  animals  of  the  Oolite  ?  What  were 
some  of  the  principal  terrestrial  reptiles  of  this  epoch  ?  Describe  the  Megalosaurus. 
Describe  the  Iguanodon. 

*  Under  the  name  of  "  beetle  stones'1  Coprolites  have  been  also  used  for  artistic  pur- 
poses. Dr.  Buckland,  the  celebrated  English  geologist,  had  a  table  in  his  drawing-room 
that  was  made  entirely  of  these  fossils,  and  was  often  much  admired  by  persons  who  had 
not  the  least  idea  of  what  they  were  looking  at.  "  I  have  seen,"  says  his  son,  "  in  actual 
use,  ear-rings  made  of  the  polished  portions  of  Coprolites  (for  they  are  as  hard  as  mar- 
ble); and,  while  admiring  the  beauty  of  the  wearer,  have  made  out  distinctly  the  scales 
and  bones  of  the  fish  which  once  formed  the  dinner  of  a  hideous  reptile,  but  now  hung 
pendulous  from  the  ears  of  an  unconscious  belle,  who  had  evidently  never  read  or  hear4 
of  such  productions." — Buckland's  Curiosities  of  Natural  History. 


262         FIKST     PRINCIPLES     OF     GEOLOGY. 

ties,  in  all  probability,  resembled  the  unwieldy  contour  of  the  rhinoceros  or 
hippopotamus,  and  were  supported  by  short,  stout  feet  The  fore  feet  ap- 
pear to  have  been  less  bulky,  and  to  have  been  adapted  for  seizing  and 
pulling  down  the  foliage  and  branches  of  trees ;  some  of  its  claws  which  have 
been  found  being  more  than  five  inches  long,  and  three  inches  broad.  Upon 
its  snout  it  carried  a  short,  thick  horn. 

Pterodactylc , — But  the  most  wonderful  animal  of  this,  or  any  other 
age,  was  the  Pterodactyle  (G-r. Diving-fingered),  or  flying  reptile — a  creature 
which  was  not  altogether  unlike  the  fabled  dragon  of  the  Middle  Ages.  It 
had  the  head  and  neck  of  a  bird,  the  jaws  and  teeth  of  a  crocodile,  the  wings 
of  a  bat,  and  the  body  and  tail  of  a  mammal.  It  was  not,  however,  a  bird, 
or  one  of  the  family  of  bats,  but  a  true  reptile,  and,  in  all  probability,  could 
walk,  fly,  or  swim,  as  its  necessities  might  require.  Kg.  173  represents  one 
of  the  most  perfect  fossil  skeletons  of  this  reptile,  and  Fig.  174  the  supposed 
appearance  of  the  living  animal 

FIG.  173.  FIG.  174. 


The  size  of  the  Pterodactyle  may  be  inferred  from  the  circumstance  that 
the  wings  of  one  specimen  which  has  been  found  must  have  had  a  spread  of 
not  less  than  twenty-seven  feet,  wjiile  the  spread  of  the  wings  of  the  great 
condor  of  the  Andes— the  largest  of  flying  birds — does  not  exceed  twelve 
feet. 

287.  The  We  aid  en, — The  most  perfect  specimens  of  these  huge  rep- 
tiles of  the  age  of  the  Oolite  have  been  obtained  from  that  portion  of  the 
system  which  is  known  as  the  "  Wealden"— a  deposit  of  strata  typically  de- 
veloped in  the  southeast  of  England.  In  this  locality,  the  group  of  the 
Wealden  appears  to  be  the  fossil  delta  of  an  ancient,  far-flowing  river* — a  delta 
as  large  as  that  of  the  Ganges  or  the  Mississippi.  The  strata  of  this  delta, 

QUESTIONS.— What  was  the  character  of  the  Pterodactyle?  What  is  said  of  the  for- 
mation of  the  Wealden  in  England  ? 

*  Fig.  175,  designed  by  the  late  Sir  Henry  de  la  Beche  (a  distinguished  English  geolo- 
gist), and  taken  from  Buckland's  "  Curiosities  of  Natural  History,"  represents  the  condi- 
tion of  things  which  may  be  supposed  to  have  existed  at  the  month  or  estuary  of  this 
river  of  the  Wealden,  or  upon  the  adjacent  ocean  coast.  In  the  center  of  the  plate,  at 
Fig.  1,  is  seen  the  Ichthyosaurus,  which  has  caught  and  is  about  to  devour  a  Plesiosau- 


OOLITIC,     OR     JURASSIC     SYSTEM.          263 
FIG.  175. 


rus.  Fisrs.  5  and  8  represent  other  Ichthosauri — one  in  the  act  of  devouring  a  fish, 
and  the  other  a  belemnite  animal,  or  cuttle  fish. — (The  evidence  that  the  Ichthyosauri 
preyed  upon  these  two  animals  is  derived  from  the  fact  that  their  coprolites  often  contain 
the  scales  of  the  one,  and  are,  not  unfrequently,  also  colored  by  the  inky  secretions  of  the 
other.)— Plesiosauri  are  also  figured,  one  of  which  has  caught  a  Pterodactyle  (see  Fig.  4), 
whose  frightened  companions  are  wheeling  about  in  the  air  overhead.  Sailing  along  the 
surface  of  the  sea,  upon  the  extreme  right  of  the  picture,  are  seen  a  fleet  of  ammonite 
shells.  Fig.  6  represents,  growing  upon  the  bottom  in  great  luxuriance,  a  specimen  of 
crinoid,  or  stone-lily.  The  land  bears  the  peculiar  vegetation  of  the  Oolite,  and  is  tenant- 
ed by  terrestrial  reptiles.  Finally,  at  the  bottom  of  this  primeval  sea  are  strewed  the 
bones  and  carcasses  of  its  inhabitants— reptiles,  fishes,  and  shells— where  they  would  be- 
come, in  the  reality,  gradually  covered  with  mud,  and  converted  into  true  fossils. 


264       FIRST     PRINCIPLES     OF     GEOLOGY. 


which  in  some  places  exceed  1,000  feet  in  thickness,  contain  fresh  water 
shells,  drift-wood,  the  bones  of  the  huge  terrestrial  reptiles  above  described, 
and,  in  short,  all  the  sweepings  of  a  great  river,  mingled  and  entombed  in 
sediments  with  marine  shells,  Crustacea,  and  the  bones  of  fishes  and  of 
gigantic  marine  reptiles.  "What  part  of  the  earth's  surface  presented  the  dry 
"*  land  through  which  this  river  held  its  course  no  one  can  tell  for  certain ;  but  it 
has  been  surmised,  that  it  flowed  from  a  point  somewhere  in  the  vicinity  of 
the  present  island  of  Newfoundland,  and  across  lands  now  submerged  be- 
neath the  Atlantic.  But  through  whatever  unknown  continent  this  old  and 
nameless  river  flowed,  "we  know,"  says  Hugh  Miller,  "that  its  banks  were 
covered  with  forests  of  coniferous  and  cycadaceous  trees,  and  with  arborescent 
ferns,  and  were  haunted  by  gigantic  reptiles,  rivaling  in  bulk  the  elephant 
and  the  mammoth.  Its  waters  were  inhabited  by  amphibia?  of  the  same 
great  class,  chiefly  crocodiles  and  turtles  of  extinct  species  and  types ;  by 
numerous  fishes  of  the  old  ganoid  order ;  and  by  shells,  whose  families  still 
exist  in  our  pools  and  rivers,  though  the  species  are  all  extinct.  Winged 
reptiles,  too,  occasionally  flitted  amid  its  woods,  or  sped  over  its  broad 
bosom ;  and  insects,  of  the  same  family  as  our  dragon-flies  darted  over  it  on 
wings  of  delicate  gauze,  in  search  of  their  prey." 

FIG.  176. 


288.  Insects, — During  the  Oolitic  epoch,  the  number  of  insect  species 
greatly  increased — so  much  so,  that  insects  are  believed  to  have  formed,  in 
part,  the  food  of  some  species  of  the  flying  reptiles.  In  certain  calcareous  strata 
of  the  European  Lias,  remains  of  insects  as  wing-cases,  etc.,  occur  in  such 
numbers  that  the  deposits  in  question  havq  received  the  name  of  the  "  In- 

QUESTION.— What  is  said  of  the  insect  life  of  the  Oolitic  epoch  1 


OR     JURASSIC     SYSTEM.          265 

sect  Limestone;"  and  Fig.  176,  which  represents  a  fossil  dragon-fly  from  the 
limestone  of  Solenhofen,  Germany,  gives  some  idea  of  the  perfection  in  which 
these  fossils  are  not  unfrequently  found.  In  addition  to  dragon-flies,  the  fol- 
lowing other  species  of  Oolitic  insects  are  thus  enumerated  by  a  recent  au- 
thority: "Ants  were  common,  as  were  also  crickets,  grasshoppers,  beetles, 
two-winged  flies,  and,  in  species  distinct  from  the  carboniferous  ones,  the 
disgusting  cockroaches ;  and,  for  the  first  time,  amid  the  remains  of  a  flora, 
that  seems  to  have  had  its  few  flowers — though  flowers  could  have  formed 
no  conspicuous  feature  in  an  Oolitic  landscape — we  detect,  in  a  few  broken 
fragments  of  the  wings  of  butterflies,  a  decided  trace  of  flower-sucking  in- 
sects." 

289.  Mammalia , — Seven  genera  of  mammalia  have  been  described  from 
the  strata  of  the  Oolitic  system.  They  were  all,  apparently,  small,  rat-like 
animals,  of  the  class  of  marsupials,  and  some  of  them  were  undoubtedly  in- 
sect-eaters. Their  remains  have  been  found  chiefly  in  the  Oolitic  rocks  of 
England. 

FIG.  m. 


290.  Birds  , — The  earliest  traces  of  the  existence  of  birds  upon  the  sur- 
face of  our  planet  are  obtained  from  a  deposit  of  red  sandstones  and  shales  in 
the  Valley  of  the  Connecticut  River,  in  New  England — a  deposit  formerly 
regarded  as  belonging  to  the  New  Red  Sandstone,  or  Triassic  System,  but 
now  generally  referred  (or  at  least  the  upper  portion  of  it)  to  the  age  of  tho 
Lias  or  Oolite. 

QTTESTION-S.— Where  do  we  find  the  earliest  evidence  of  the  existence  of  birds?  What 
is  said  of  the  geological  age  of  the  Connecticut  River  sandstones? 

12 


266       FIRST     PRINCIPLES     OF     GEOLOGY. 

No  certain  fragments  of  the  skeletons  of  birds,  however,  have  as  yet  been 
found  in  any  geological  formation  older  than  the  Wealden  (the  uppermost 
group  of  the  Oolitic  system) ;  but  on  the  successive  layers  of  the  deposit  of 
shales  and  sandstones  above  referred  to  (which  extends  in  the  Valley  of  the 
Connecticut  Kiver,  from  the  northern  part  of  Massachusetts,  southward  for  a 
distance  of  ninety  miles),  impressions  of  the  feet  of  birds  and  other  animals 
occur  in  great  numbers.  The  general  appearance  of  these  remarkable  fossils 
is  represented  in  Fig.  11*7. 

The  aggregate  thickness  of  the  successive  layers  of  shale  and  sandstone, 
on  the  surfaces  of  which  these  tracks  are  impressed,  has  been  estimated  to  ex- 
ceed a  thousand  feet.  In  many  instances,  the  weight  of  the  animal  bent 
downward  several  layers  of  muddy  sediment — so  that  now,  when  the  rock, 
resulting  from  the  consolidation  of  the  sediment,  is  split  open,  we  find  the 
impressions  of  its  feet  preserved,  more  or  less  distinctly,  on  a  number  of  suc- 
cessive layers — the  upper  surfaces  showing  the  tracks  depressed,  and  the  lower 
the  tracks  in  relief.  Fig.  178  represents  a  curious  example  of  this  nature  in 
the  cabinet  of  Amherst  College,  where  the  impressions  of  two  tracks,  by  an 
ingenious  device  of  Prof.  Hitchcock,  are  shown  to  be  continued  through  five 
successive  layers — the  aggregate  thickness  of  which  is  five  inches. 

FIG.  178. 


The  birds  which  impressed  these  tracks  (on  an  original  muddy  or  sandy 
shore),  were  apparently,  for  the  most  part,  long-legged  birds,  with  but  three 
toes  on  each  foot — like  the  cranes,  herons,  snipes,  or  ostriches  of  the  present 
day.  Some  of  the  impressions  are  of  such  singular  distinctness  that  not  only 
are  the  marks  of  every  claw  and  joint  discernible  on  the  stone  surface,  but 
even  the  minute  irregularities  of  the  skin  on  the  underside  of  the  foot  re- 
main as  sharply  defined  as  if  the  impress  had  been  made  upon  wax.  Fig. 
179  represents  a  track,  showing  the  joints  (or  phalanges)  of  the  toes,  and  also 
the  marks  of  a  shower  of  rain  which  fell  upon  the  muddy  surface  about  the 
time  the  track-making  bird  passed  over  it. 

QUESTIONS.— What  is  the  thickness  of  the  layers  in  which  the  tracks  occur?  Hotf 
^ere  these  tracks  formed  ?  What  is  said  of  their  distinctness  ? 


OOLITIC,     OE     JURASSIC     SYSTEM. 


267 


291.  Tracks,  which  are  believed  to  have  been  made  by  thirty-one  different 
species  of  birds,  have  thus  far  been  described  by  Prof.  Hitchcock,  from  the 
shales  and  sandstones  of  the  Valley  of  the  Connecticut  River.  Some  of  them 
are  very  small,  as  if  made  by  birds  no  larger  than  sparrows,  while  others  are 
of  gigantic  size,  and  equal  the  footprints  of  the  largest  quadrupeds.  One  slab, 
in  the  cabinet  of  Amherst  College,  shows  footprints  which  measure  eighteen 
inches  from  the  heel  to  the  end  of  the  middle  claw,  nearly  thirteen  inches  in 
greatest  breadth,  and  a  stride  -p1Q>  ^^ 

(judging  from  the  distance  of 
the  tracks  apart  in  a  straight 
line)  of  fro,n  three  to  five  feet. 

When  these  tracks  were  first 
discovered,  it  was  doubted — 
especially  by  reason  of  the  great 
size  of  some  of  them — whether 
they  could  have  b3en  imprinted 
by  birds;  but  at  the  present 
time,  most  geologists  and  com- 
parative anatomists  are  entirely 
satisfied  that  they  were  really 
made  by  the  class  of  .animals 
in  question.  Moreover,  our 
wonder  at  the  size  of  the  im- 
pressions has  been  somewhat 
lessened,  by  the  discovery  that 
there  existed  upon  the  islands 
of  New  Zealand,  within  a  com- 
paratively recent  period,  a  race 
of  gigantic  birds,  but  little,  if 
any,  inferior  in  size  to  those 
which  are  believed  to  have  lived  in  New  England  during  the  Oolitic  or 
Triassic  ages — some  bones  having  been  brought  from  New  Zealand  which 
belonged  to  birds  over  eleven  feet  in  height.* 

292.  Besides  the  tracks  of  birds,  there  are  also  found  upon  the  strata-sur- 
faces of  the  same  formation,  impressions  of  the  feet  of  many  other  animals — 
such  as  marsupials,  lizards,  tortoises,  batrachians  (frogs),  and  animals  that 
walked  upon  two  legs  and  yet  dragged  a  tail  behind  them;  together  with 
traces  of  markings  apparently  made  by  insects,  worms,  and  Crustacea — in  all, 
eighty-eight  different  kinds  of  imprints  other  than  those  of  the  feet  of  birds. 

Fig.  180  represents  tracks  found  at  South  Hadley,  Mass.,  which  are  the 

QUESTIONS.— What  of  their  number  ?  What  of  their  size?  What  interesting  fact  re- 
specting the  existence  of  enormous  birds  has  recently  been  made  known  ?  What  other 
impressions  besides  those  of  the  feet  of  birds  are  found  upon  the  strata  of  the  Connecti- 
cut River  sandstones  ?  What  is  said  of  the  number  and  size  of  these  impressions  ? 


For  further  notice  of  these  discoveries,  see  page  317. 


268 


FIRST     PRINCIPLES    OF     GEOLOGY. 


largest  as  yet  discovered,  and  are  believed  to  have  been  made  by  a  huge 
frog-like  animal.  Each  track  is  twenty  inches  long,  fifteen  inches  wide,  and 
covers  upward  of  a  square  foot  of  surface.  Upon  the  same  slab — preserved 
in  the  cabinet  of  Amherst  College — are  also  many  other  smaller  tracks  (ap- 
parently made  by  birds)  crossing  each  other  and  crowded,  like  impressions 
of  feet  upon  the  shores  of  a  muddy  pool  which  ducks  and  geeso  have  fre- 
quented. 

FIG.  180. 


293.  Condition  of  the  World  during  the  Oolitic  Epoch,— 

Respecting  the  condition  of  the  world  during  the  deposition  of  the  strata  in- 
cluded in  the  Oolitic  or  Jurassic  system,  everything  testifies,  as  has  been 
already  intimated,  to  the  universal  existence  of  a  genial,  if  not  of  a  tropical 
climate.  Indeed,  according  to  Prof.  Owen,  a  close  correspondence  may  be 
traced  between  the  "land  of  the  Oolite"  and  the  condition  of  things  which 
now  prevails  in  Australia.  Thus,  the  climate  of  this  great  "  island  continent" 
is  semi-tropical ;  "among  its  plants,  the  tree-ferns,  cycadaceos,  and  other  Oolitic 

QUESTION. — What  -was  supposed  to  bo  the  condition  of  the  world  during  the  Oolitic 
epoch  ? 


OR     CRETACEOUS     SYSTEM.        269 

genera  still  have  representatives  ;  many  of  the  fish  and  mollusca  which  in- 
habit its  waters  belong  to  the  same  families  which  prevailed  in  the  ocean 
of  the  Oolite,  and  are  unlike  any  which  are  known  elsewhere ;  while  its 
largest  native  land  animals  are  of  the  lowest  class  of  mammalia,  viz.,  marsu- 
pials (kangaroos,  etc.). 

During  the  Oolitic  epoch,  it  seems  certain  also  that  a  genial  temperature 
prevailed  in  the  Arctic  regions ;  that  its  lands  were  covered  with  plants  like 
those  of  tropical  countries,  and  inhabited  by  lizard-like  forms  and  insects  ; 
while  its  rivers,  bays,  and  seas  abounded  with  huge  reptiles,  fishes,  shells, 
Crustacea,  and  corals.  Theso  startling  conclusions  are  based  on  the  reports 
of  recent  explorers,  that  the  rocks  of  the  Arctic  zone,  in  many  localities,  are 
full  of  Oolitic  fossils.  Thus,  Capt.  M'Clintock  obtained  from  strata,  in  ''Prince 
Patrick's  Land,"  Ammonites,  Belemnites,  and  bones  of  reptiles;  and  another 
of  the  expeditions  sent  out  in  search  of  Sir  John  Franklin  brought  home, 
from  the  same  regions,  a  part  of  the  skeleton  of  an  Ichthyosaurus. 


CHALK,     OR     CRETACEOUS     SYSTEM. 

294.  This  system  derives  its  name  from  the  great  de- 
posits of  white  chalk  (Lat.,  creta)  which  are  included  in 
it,  and  constitute  its  most  notable  feature. 

The  rocks  of  the  system  are  chalk  and  other  calcareous  deposits,  sands, 
sandstones,  clays,  and  marls — all  of  marine  origin.  Beds  of  pure  chalk  are 
confined  to  the  upper  portions  of  the  system ;  while  the  lower  are  especially 
(but  not  exclusively)  characterized  by  the  presence  of  beds  of  sand  and  of 
sandstones,  which  have  a  peculiar  greenish  appearance.  Hence,  it  is  com- 
mon to  divide  the  Cretaceous  system  into  two  great  groups — the  upper  being 
termed  the  "  Chalk,"  and  the  lower  the  "  GreensancL" 

295.  Distribution . — The  Cretaceous  system  is  finely  developed  in  the 
south  of  England,  where  it  has  been  more  carefully  studied,  perhaps,  than 
in  any  other  country.    The  celebrated  chalk  cliffs  of  Dover,  on  the  English 
Channel,  are  examples  of  its  development.     It  spreads  over  wide  areas  in 
France  and  Germany,  and  forms  a  part  of  the  great  mountain  chains  of  the 
Alps,  Pyrenees,  and  Carpathians.     Cretaceous  rocks  also  occur  in  India, 
South  Africa,  and  South  America. 

In  North  America,  the  Cretaceous  system  occupies  a  large  area  of  surface. 
Commencing  at  the  islands  of  Nantucket  and  Martha's  Vineyard  (the  cliffs  at 
Gay  Head,  on  the  latter  island,  being  probably  of  this  age),  it  is  largely  de- 

QTTESTIONS. — What  evidence  have  we  that  a  mild  climate  prevailed  at  this  age  in  the 
present  Arctic  latitudes  ?  From  what  does  the  Cretaceous  system  derive  its  name  ?  What 
are  the  principal  constituent  rocks  of.  the  system  ?  How  is  it  usually  divided?  What  is 
said  of  the  distribution  of  the  Cretaceous  system  in  Europe  ? 


270 


FIRST     PRINCIPLES     OF     GEOLOGY. 


veloped  in  New  Jersey ;  and  from  thence  it  extends  continuously  along  the 
Atlantic  and  Gulf  Coast — through  Delaware,  Maryland,  Virginia,  the  Caro- 
linas,  Georgia,  Alabama,  and  Texas — to  Mexico ;  "  and  then  covers  nearly 
one-third  of  the  width  of  the  continent,  from  near  the  Gulf  of  Mexico  to 
British  North  America,  with  occasional  interruptions." 

The  true  chalk,  which  occurs  so  abundantly  in  Europe,  has  not  yet  been 
found  among  the  Cretaceous  rocks  of  North  America,  but  the  peculiar  green- 
sands  of  this  system  are,  however,  present  in  some  localities,  and  may  be 
seen  especially  to  advantage  in  eastern  New  Jersey. 

Near  the  sources  of  the  Red  Eiver  there  are  immense  deposits  of  gypsum 
("  Plaster  of  Paris"),  which  are  believed  to  be  of  the  Cretaceous  age,  and  are 
probably  the  largest  in  the  world. 

FIG.  181. 


296.  Origin  of  Chalk  a^nd  Grecnsand, — "White  chalk  (well 
known  as  a  material  for  marking)  is  a  soft,  pulverulent  carbonate  of  lime, 
and  can  bo  converted,  like  ordinary  limestone,  by  calcination,  into  quick- 
lime.* In  Europe,  it  constitutes  a  large  part  of  the  Cretaceous  system; 
and  has  been  traced,  in  one  direction,  from  the  north  of  Ireland  to  South- 

QUESTIONS. — What  in  North  America  ?  Is  true  chalk  found  in  this  country?  What  is 
chalk  ?  Under  what  circumstances  does  it  occur  ? 


*  The  term  "  chalk"  is  often  applied  to  various  substances  which  arc  in  no  sense  of  thg 
word  limestones :  as  "  lied  Chalk,"  a  natural  clay  containing  a  considerable  percentage 
of  oxyd  of  iron;  " French  Chalk"  a  variety  of  steatite,  or  soapstone;  and  " Brown 
Chalk"  a  familiar  uar.ic  for  umber." 


OR   ^CRETACEOUS     SYSTEM.        271 

ern  Russia — a  distance  of  about  1,200  miles;  and,  in  another  direction, 
from  the  south  of  Sweden  to  the  southeast  of  France — a  distance  of  about 
900  miles;  and  there  are  extensive  districts  in  both  France  and  England 
where  its  average  thickness  is  not  less  than  a  thousand  feet.  All  geologists 
are  agreed  that  this  immense  deposit  of  this  singular  variety  of  limestone  was 
formed  at  the  bottom  of  an  ocean  "  of  a  very  considerable  depth,  and  of  such 
extent  that  it  must  have  covered,  for  many  ages,  the  greater  part  of  what  is 
now  Central  and  Southern  Europe;"  but  concerning  the  exact  manner  of 
its  production  there  is  considerable  doubt.  "The  only  analogous  product  of 
the  present  day  occurs  on  a  comparatively  small  scale  among  the  coral  reefs 
and  islands  of  the  Pacific,  where  there  is  constantly  forming  an  impalpable 
white  mud,  derived  from  the  coral,  which,  in  dried  specimens,  cannot  be  dis- 
tinguished, by  the  unassisted  eye,  from  masses  of  soft  chalk."  True  chalk, 
however,  differs  widely  from  its  modern  representative,  inasmuch  as  it  is 
composed,  to  the  extent  of  about  one  half  of  its  entire  bulk,  of  the  shells  of 
microscopic  animalcules,  so  extremely  minute,  that  every  cubic  inch  of  chalk 
has  been  estimated  to  contain  the  remains  of  over  a  million  different  organ- 
isms. "If  our  eyes  could  bo  suddenly  endowed  with  a  high  microscopic 
power,"  says  Hugh  Miller,  "the  white  line  which  we  draw  with  chalk  along 
a  board  would  resemble  a  part  of  a  wall  of  a  grotto,  covered  over  with  shells." 
Fig.  181  represents  an  appearance  of  chalk,  as  viewed  under  a  microscope. 

The  Grecnsand.  which  gives  name  to  the  lowest  group  of  the  Creta- 
ceous system,  consists  of  small,  round  granules,  of  a  greenish  color,  which 
are  commonly  intermixed  with  variable  proportions  of  clay  and  siliceous 
sand.  These  granules  are  mainly  composed  of  silica  and  iron  (forming  a 
silicate  of  iron)  and  potash ;  and  owing  especially  to  the  presence  of  the 
latter  ingredient,  they  possess  valuable  fertilizing  properties.*  In  New 
Jersey,  where  the  greensand  beds  have  an  aggregate  thickness  of  about  100 
feet,  it  is  dug  (under  the  name  of  marl)  from  pits  during  the  winter  season, 
and  spread  upon  the  fields,  preparatory  to  being  plowed  in.  Twenty  loads 
to  the  acre  are  said  to  produce  more  valuable  results  than  200  loads  of  good 
stable  manure ;  the  effect  being  experienced  with  the  first  crop,  and  continu- 
ing for  several  years  afterwards. 

The  origin  of  these  greensand  grains  was  for  a  long  time  a  matter  of 
doubt  among  geologists,  but  within  a  comparatively  recent  period  micro- 
scopic investigations  have  shown  that  they  are,  in  many  instances,  the  casts 
(models)  of  microscopic  shells  of  the  order  Foraminifera,f  and  of  some  other 

QUESTIONS.— Is  there  any  substance  analogous  to  chalk  now  forming  ?  In  what  respect 
does  chalk  differ  from  any  similar  modern  products?  What  is  the  so-called  "  green- 
sand?"  What  is  said  of  its  value  as  a  fertilizing  agent? 

*  The  average  composition  of  the  greensands  of  New  Jersey  is  as  follows :  Silica,  forty- 
seven  to  fifty-one  per  cent. ;  protoxyd  of  iron,  twenty  to  twenty-four ;  alumina,  six  to 
nine  ;  potash  ten  to  twelve.  In  addition,  the  greensand  strata  always  abound  in  organic 
remains — shells,  fragments  of  bones,  etc. — which,  by  their  decomposition,  become  valu- 
able fertilizing  auxiliaries. 

t  The  Foraminifera  are  an  order  of  animals  of  low  organization,  belonging  to  the  class 
Protozoa— BCQ  §  200,  page  190 ;  and  §  G8,  page  5S. 


272        FIRST     PRINCIPLES     OF     GEOLOGY. 


organic  bodies.  "  The  shells  themselves  have  disappeared ;  but  the  internal 
form  of  their  cavities  has  been  retained  by  a  silicate  of  iron,  which  took  the 
place  of  the  animal  bodies,  as  these  decayed,  and  retained  their  shapes.  So 
perfectly  has  this  been  done,  that  even  the  very  finest  canals  of  the  cell- 
walls,  and  all  their  connecting  tubes,  are  thus  petrified  and  separately  ex- 
hibited." Eecent  soundings  by  the  United  States  Coast  Survey  have,  more- 
over, brought  up  from  the  depths  of  the  ocean — in  the  Gulf  Stream  and  the 
Gulf  of  Mexico— not  only  grains  of  greensand,  having  the  form  of  well-de- 
iined  casts  of  foraminifera  and  minute  molluscs,  but  also  perfectly  preserved 
shells  of  the  same  species  of  animals — thus  showing  that  the  production  of 
greeusand  is  still  going  on,  in  some  seas,  by  the  same  agencies  which  pro- 
duced it  in  ancient  geological  periods. 

FIG.  182. 


Flints  . — A  remarkable  feature  of  the-  chalk  beds  of  Europe  is  the  occur- 
rence in  them  of  nodular  masses  of  nearly  pure  flint  (silica),  of  very  irregular 
and  often  fantastic  forms,  and  of  variable  magnitude.  These  are  generally 
desposited  in  horizontal  layers  (see  Fig.  182),  and,  although  very  numerous, 
are  rarely  in  contact  with  each  other — each  being  completely  enveloped  by 
the  chalk.*  The  explanation  given  concerning  the  formation  of  these  singu- 
lar masses,  is,  that  they  were  produced  by  a  chemical  aggregation  of  particles 
of  silica,  originally  held  in  solution  in  tho  mass  of  the  chalk.  But  whenco 
the  origin  of  this  silica  in  the  midst  of  a  substance  so  different  from  it  as 
chalk?  Ehrenberg,  the  eminent  microscopist,  has  suggested  that  it  was  de- 
rived from  the  siliceous  coverings  of  microscopic  animals ;  and,  in  confirma- 
tion of  his  views,  he  states,  that  while  chalk  with  flints  abounds  in  the  north 
"  of  Europe,  and  without  flints  in  the  south,  silicious  animalcules  are  wanting 
in  the  northern  chalk,  and  are  present  in  great  quantities  in  the  southern ; 

QUESTIONS. — What  is  known  respecting  its  origin  ?    "What  is  said  respecting  the  occur- 
rence of  flint  nodules  in  the  chalk-beds  of  Europe  ? 


*  These  flints  of  the  chalk,  calcined  and  ground,  furnish  the  finest  material  for  the 
manufacture  of  china  ware,  porcelain,  and  flint  glass,  and,  before  the  invention  of  per- 
cussion caps,  were  in  demand  for  the  manufacture  of  gun-flints. 


CHALK,     OR     CRETACEOUS     SYSTEM.       273 

thus  leading  to  the  conclusion,  that  in  the  one  case  the  silicious  skeletons 
have  been  left  in  their  natural  form,  while  in  the  other  they  have  been  dis- 
solved chemically,  and  aggregated  upon  the  principle  of  chemical  affinity  into 
nodules  cf  flint.  But  whatever  may  have  been  the  source  of  the  silica  of  the 
chalk  flints,  it  appears,  in  almost  every  instance,  to  have  concentrated  upon 
some  organic  substance  in  the  ancient  ocean;  and,  consequently,  when  a 
flint  nodule  is  now  broken  open,  it  is  found  to  inclose  the  remains  of  sponges, 
echinoderms,  corals,  and  other  marine  organisms,  which  are  often  hi  the 
most  perfect  state  of  preservation. 

297.  Life  of  the  Cretaceous  Epoch, — The  organic  re- 
mains found  in  the  rocks  of  the  Cretaceous  system  are 
eminently  marine  ;  comprising  numerous  microscopic  or- 
ganisms, fucoids  (sea-weeds),  sponges,  corals,  star-fishes, 
molluscs,  Crustacea,  fishes,  and  reptiles. 

FIG.  183. 


FIG.  184. 


If  we  compare,  however,  the  fossils  of  the  upper  Cretaceous  strata  with 
those  found  in  the  Oolitic  rocks  below,  a  complete  change  of  species  will  be 
noticed.  There  were  ammonites,  and  belemnites,  and  many  other  shells 
with  common  generic  names  in  both  eras,  but  the  cretaceous  species  are 
obviously  different  from  those  of  the  Oolite.  And  so  with  the  radiata,  and  tho 
fish,  and  the  reptiles,  and  all  other  classes  and  orders  of  animals  and  plants, 
as  far  as  their  remains  have  as  yet  been  described. 

Figs.  183  and  184  represent  two  of  the  characteristic  shells  of  the  Creta- 

QUESTIONS — What  is  supposed  to  have  been  their  origin  ?  What  is  said  of  the  organic 
remains  found  in  tho  Cretaceous  system  ?  Are  the  fossils  of  the  Cretaceous  and  Oolitic 
eystcms  alike  ? 

12* 


274       FIRST     PRINCIPLES     OF     GEOLOGY. 

ceous  system — Fig.  183  being  a  turrilite,  which  may  be  described  as  an  am- 
monite twisted  in  a  spiral  instead  of  a  disc-like  form  ;  and  Fig.  184,  a  scaphite, 
in  which  the  coils  of  the  ammonite  are  partially  unrolled  and  then  turned  up 
at  the  end,  so  as  to  give  the  shell  a  boat-like  form. 

298.  Fishes, — The  remains  of  not  less  than  seventy-eight  genera  of 
fishes  have  been  obtained  from  the  Cretaceous  system.  The  majority  of 
these  are  of  the  old  orders  of  placoids  and  ganoids,  but  during  this  era  the 
ctenoid  and  cycloid  orders  (to  which  most  existing  fishes  belong)  were  also 
ushered  into  existence — their  remains  being  found,  for  the  first  time,  in 
Cretaceous  strata.  And  from  this  epoch  onward,  the  orders  of  placoid  and 
ganoid  fishes  gradually  diminish  and  fade  out,  while  the  ctenoids  and  cycloids 
rapidly  develop,  until,  at  present,  they  seem  to  have  reached  their  culminating 
poin^  and  many  times  exceed  in  number  and  importance  all  other  fishes.* 

FIG.  185. 


299.  Reptiles, — The  reptiles,  so  numerous  in  the  two  preceding  eras, 
appear  to  have  greatly  diminished  in  numbers  during  the  Cretaceous  epoch. 
The  ichthyosaurus  and  the  plesiosaurus  continued  to  exist,  but  their  rule 
over  the  ocean  was  shared  by  a  new  gigantic  lizard-like  reptile — the  Mosa- 
saurus.  This  animal  was  about  twenty-five  feet  in  length,  and  had  probably 
paddles  instead  of  legs,  and  a  tail  suited  to  assist  it  powerfully  in  swimming. 
A  perfect  specimen  of  its  head,  which  was  found  embedded  in  limestone,  at 

QUESTIONS.— What  is  known  respecting  the  fishes  of  this  epoch  ?  What  is  said  of  the 
reptile  life  of  this  epoch  ? 


*  At  the  present  time  the  sturgeons  and  the  gar-pikes  (of  our  -western  rivers)  are  the 
most  familiar  representatives  of  the  ganoid  order  of  fishes  ;  and  the  skates,  dog-fish,  and 
sharks,  of  the  placoid  order; — "  they  are  but  the  inconsiderable  fragments  of  dynasties 
which  were  once  coextensive  with  every  sea,  and  predominated  during  the  unreckoned 
ages  which  extended  From  the  times  of  the  Lower  Devonian  until  those  of  the  Chalk.1' 


OR     CRETACEOUS     SYSTEM.        275 

Maastricht,  Belgium  (seo  Fig.  185),  measured  four  and  a  half  feet  long,  by 
two  and  a  half  broad.*  Its  teeth  are  found  in  the  Cretaceous  deposits  of  this 
country  also. 

In  1858,  there  was  also  found  in  the  greensands  of  Camden  County,  New- 
Jersey,  the  remains  of  a'  huge,  saurian  reptile — the  Hadrosaurus — which  was 
closely  allied  to  the  iguanodon,  and  is  proved,  by  the  structure  of  its  teeth, 
to  have  been  herbivorous  (plant-eating).  The  length  of  the  Hadrosaurus  is 
estimated,  by  Prof.  Leidy,  to  have  been  about  twenty-five  feet ;  but  a  better 
idea  of  its  enormous  size  may  be  gained  from  the  statement,  that  its  thigh 
bone  is  nearly  one-third  longer  than  that  of  the  mastodon.  Its  hind  leg  bones, 
when  put  together,  measure  seven  feet,  upon  which  the  pelvis,  back-bone, 
and  upper  skin  would  still  go  on,  making  it  nine  or  ten  feet  high  upon  the 
haunches.  The  animal  was  probably  amphibious.  Its  bones  can  be  seen 
at  the  Academy  of  Natural  Sciences  in  Philadelphia, 

The  remains  of  crocodiles  and  turtles  are  also  common  in  the  rocks  of  the 
Cretaceous  system.  Fig.  186  represents  a  specimen  of  fossil  tortoise,  from 
the  chalk  of  England. 

300.  Concerning  the  land  which  skirted  the  ocean  of  the  Chalk  epoch,  or 
of  its-  productions,  we  know  almost  nothing.  The  general  indications  are, 
that  the  climate  was  genial,  and  favorable  to  the  production  of  cycadaceas, 
palms,  arid  coniferous  plants,  on  land,  and  of  corals,  gigantic  reptiles,  and 
turtles,  in  the  waters.  In  the  Cretaceous  deposits  of  this  country,  frag- 
ments of  fossil  wood  and  leaves  are  by  no  means  uncommon,  and  the  micro- 
scopic structure  of  wood  from  the  greensands  of  New  Jersey  does  not  differ 
materially  from  that  of  the  pine  trees  which  now  grow  in  the  same  locality. 

QUESTIONS. — What  were  the  most  remarkable  Cretaceous  reptiles?  Have  any  gigantic 
Cretaceous  reptiles  been  found  in  the  United  States?  What  is  known  respecting  the 
dry  land  of  the  Chalk  epoch? 


*  The  history  of  this  remarkable  fossil  may  be  said  to  form  a  part  of  the  romance  of 
geological  history,  and  is  related  by  Mr.  Mantell,  as  follows :  In  1TTO,  the  workmen  em- 
ployed in  blasting  limestone  from  some  celebrated  quarries  at  Maestricht,  in  the  Kingdom 
of  Belgium,  perceived,  to  their  astonishment,  the  jaws  of  an  enormous  animal  attached 
to  the  roof  of  a  cavern  which  they  had  excavated.  The  discovery  was  immediately  made 
known  to  M.  Hoffman,  a  naturalist  of  the  town,  who  repaired  to  the  spot,  and  for  weeks 
presided  over  the  arduous  task  of  separating  from  the  rock  the  mass  of  stone  containing 
the  remains.  His  labors  were  at  length  repaid  by  the  successful  extraction  of  the  speci- 
men, which  he  conveyed  in  triumph  to  his  honse.  Unfortunately  the  Dean  of  the  Cathe- 
dral claimed  the  fossil  in  right  of  being  lord  of  the  manor,  and  succeeded,  by  a  law  suit, 
in  obtaining  the  precious  relic.  It  remained  in  his  possession  for  many  years,  and  Hoff- 
man died  without  regaining  his  treasure,  or  receiving  any  compensation.  The  French 
revolution  broke  out,  and  the  armies  of  the  Republic  advanced  to  the  gates  of  Mses- 
tricht ;  the  town  was  bombarded,  but  by  desire  of  a  committee  of  scientific  men,  who  ac- 
companied the  French  troops,  the  artillery  was  not  allowed  to  play  on  that  part  of  the 
city  in  which  the  celebrated  fossil  was  known  to  be  contained.  In  the  meanwhile,  the 
ecclesiastic,  shrewdly  suspecting  why  such  peculiar  favor  was  shown  to  his  residence, 
concealed  the  specimen  in  a  secret  vault ;  but  when  the  city  was  taken  the  French  au- 
thorities compelled  him  to  give  up  his  ill-gotten  prize,  which  was  immediately  trans- 
mitted to  the  Jardin  des  Plantea,  at  Paris,  where  it  now  forms  one  of  the  most  striking 
objects  in  that  magnificent  collection. 


276        FIUST      PRINCIPLES     OF     GEOLOGY. 

In  the  Cretaceous  strata  of  Europe,  the  bones  of  Pterodactyleg  and  of  true 
birds  have  been  found,  and  also  certain  remains  which  are  surmised  to  be 
those  of  monkeys. 

FIG.  186. 


301.  Close  of  the  Mesozoic  Period, — "With  the  close  of  the  Cre- 
taceous system  the  Mesozoic  period  of  geological  histor}r  terminates,  and  a 
new  order  of  things  begins.  So  abrupt,  indeed,  is  the  break  at  this  point  of 
the  geological  series,  that  of  all  the  numerous  forms  of  life  found  in  the  Tri- 
assic,  the  Oolite,  and  Cretaceous  systems,  hardly  a  single  species  crosses  the 
gap,  and  is  found  in  the  strata  of  the  succeeding  (Tertiary)  system — the  ex- 
ceptions, it  is  affirmed,  being  one  shell,  one  coral,  and  certain  microscopic 
organisms  or  infusoria.  Of  these  last,  fifty-seven  species  occurring  in  the 
chalk,  are,  according  to  Ehrenberg,  still  found  living  in  different  parts  of  the 
earth,  and  have  been  apparently  preserved  from  the  destruction  which  has 
overtaken  other  races,  by  the  very  humility  of  their  organization  and  position. 

The  characteristic  features  of  the  Mesozoic  period 
were — 

1.  The  absence  of  mammiferous  animals  from  the  earth, 
with  the  exception  of  a  few  genera  of  small  size,  belonging 
to  the  humble  class  of  marsupalia.  The  remains  of  Meso- 
zoic reptiles  have  been  often  mistaken  for  those  of  Cetacea 
(whales,  seals,  porpoises,  etc.),  but  it  is  now  generally  held 
that  none  even  of  this  class  of  marine  ^ammals  were 
called  into  existence  until  the  dawn  of  the  subsequent 
period  : — 

QUESTIONS. — What  period  closes  with  the  Cretaceous  system  ?  What  reasons  exist  for 
making  a  division  of  the  geological  series  at  this  point? 


CHALK,     OR     CRETACEOUS     SYSTEM.        277 

2.  An  immense  development  of  reptiles,  which  tenanted 
the  land  and  sea  in  such  numbers,  that  the  Mesozoic  period 
is  often  spoken  of  as  the  "reign"  or  "dynasty"  of  reptiles : — 

3.  During  the  Mesozoic  period   the  placoids  and  the 
ganoids  cease  to  be  the  sole  representative  orders  of  fishes  ; 
.and  two  new  orders — the  ctenoids  and  the  cycloids,  to 
which  the  majority  of  our  present  fishes  belong — were 
called  into  existence  : — 

4.  The  beautiful  group  of  chambered  shells,  known  as 
the  ammonites,  and  the  curious  family  of  the  belemnites, 
belong  exclusively  to  this  period  ;  while  the  other  prevail- 
ing forms  of  invertebrate  life — the  coral  animals,  the  cri- 
noids,  Crustacea,  etc. — were  characteristically  different  from 
the  Paleozoic  species. 

302.  The  action  of  igneous  forces  during  the  Mesozoic  period  was  frequent 
and  powerful,  and  was  especially  manifested  in  the  eruption  of  many  of  the 
great  masses  and  ranges  of  trap  rock  of  this  country  and  of  Europe ;  the 
molten  matter  having  risen  along  extensive  lines  in  the  earth's  crust,  and 
overflowed  and  accumulated  upon  its  surface.  Such  an  example  of  a  line 
of  eruption,  in  thia  country,  is  afforded  by  the  belt  or  range  of  trap  rocks 
which  runs  along  the  Valley  of  the  Connecticut  River — entirely  across  the 
States  of  Massachusetts  and  Connecticut — and  which  has  Mounts  "Iloly- 
oke"  and  "Tom,"  and  "East"  and  "West"  Rocks  at  New  Haven,  as  its 
most  conspicuous  elevations.  This  eruption  of  trap  is  known  to  have 
taken  place  during  the  deposition  of  those  sandstones  of  the  Connecticut 
Valley  which  afford  the  remarkable  fossil  foot-prints ;  since  the  strata  of  the 
sandstones  have,  in  some  instances,  been  penetrated  and  overflowed  by 
the  trap,  and  in  others  have  been  deposited  upon  the  igneous  rock  sub- 
sequent to  its  consolidation ;  and  as  these  sandstones  are,  undoubtedly,  of 
Oolitic  or  Triassic  age,  we  have  the  geological  date  of  the  formation  of  this 
trap  range  and  of  the  above-mentioned  mountains,  determined  with  com- 
parative certainty.  The  trap  range,  which  occupies  a  portion  of  the  South- 
ern Valley  of  the  Hudson,  and  appears  conspicuously  in  the  bold  bluff  of  the 
"Palisades,"  was  also  probably  erupted  at  the  same  epoch.  In  Europe, 
Mesozoic  traps  are  abundant ;  and,  at  about  the  close  of  the.Cretaceous  epoch, 
immense  quantities  of  basalt  were  poured  out,  covering  a  great  part  of  the 
North  of  Ireland,  and  forming  the  well-known  "Giant's  Causeway."  (See 
§  103.) 

Concerning  the  attendant  phenomena  of  these  great  eruptions,  and  the 
changes  which  they  must  have  produced  in  the  topography,  climate,  and 

QtrES-noiiS.— What  were  the  characteristic  features  of  the  Mesozoic  period  ?  What  is 
said  of  the  action  of  igneous  forces  during  this  Mesozoic  period  ? 


278         FIRST     PRINCIPLES     OF     GEOLOGY. 

organic  life  of  the  countries  affected  by  them,  we  can  probably  form  but 
little  idea.  The  mightiest  volcanic  eruptions  of  the  historical  period  are  our 
only  materials  for  comparison,  and  it  would  seem  as  if  those  portions  of  the 
earth,  through  which  the  molten  trappean  rock — now  hardened  into  moun- 
tains— rushed  in  floods  to  the  surface,  must  have  been,  for  the  tune  being, 
literally  "  lands  of  fire." 


CAISTOZOIC    PERIOD. 

303.  The  Cainozoic,  or  Recent  Life  Period,  includes  the 
Tertiary  system,  and  all  the  geological  formations  of  sub- 
sequent date,  up  to  the  present  epoch. 

TERTIARY    SYSTEM. 

304  The  earlier  geologists  divided  the  stratified  crust  of  the  earth  into 
three  great  formations,  viz.,  the  Primary  (first),  Secondary  (second),  and  Ter- 
tiary (third) ;  and  regarded  as  Tertiary  all  that  occurs  above  the  chalk.  The 
term  thus  originating,  is  still  retained,  but  the  progress  of  discovery  has  ren- 
dered it  necessary  to  restrict  and  modify  its  meaning ;  and  it  is  now  usual 
with  most  geologists  to  consider  as  Tertiary  all  those  formations  which  occur 
above  the  Cretaceous  system,  tih1  the  close  of  the  so-called  Drift  deposits;  and 
as  " Post- Tertiary  or  "Recent"  every  accumulation  which  appears  to  have 
been  formed  since  the  Drift  epoch.* 

305.  Divisions  of  the  Tertiary  System,— As  has  been  already 
stated,  it  is  generally  beh'eved  by  geologists  that  the  species  of  animals  and 
plants  inhabiting  the  earth  during  the  Mesozoic  period,  with  very  few  ex- 
ceptions, passed  out  of  existence  before  the  commencement  of  the  epoch 
represented  by  the  Tertiary  system.  "We  accordingly  find,  in  examining 
Tertiary  strata,  that  the  fossils  contained  in  them  are  not  only 'new,  but  of 
Cainozoic  type,  by  which  expression,  we  are  to  understand,  that  they  aro  all 
more  or  less  allied  to,  or  even  identical  with,  existing  genera.  In  the  oldest 
Tertiary  deposits,  or  those  which  lie  immediately  above  the  Cretaceous  sys- 
tem, there  are,  probably,  no  fossils  which  are  exactly  the  same  as  any  living 
species ;  but  as  we  ascend  in  the  series  we  find,  first  one  shell,  and  then 
another,  which  seems  actually  of  the  same  species  as  those  which  still  live ; 

QUESTION. — What  geological  formations  are  included  in  the  Cainozoic  periods  ?  What 
was  the  origin  of  the  term  Tertiary  ?  What  are  the  generally  recognized  limits  of  the 
Tertiary  system  ? 

*  Some  geologists  do  not  include  the  "Drift"  in  the  Tertiary  system ;  while  others  in- 
clude not  only  the  drift  but  every  other  accumulation  formed  subsequent  to  the  drift  up 
to  the  present  period. 


CAINOZOIC      PERIOD.  279 

until,  finally,  in  the  later  deposits  of  the  system,  the  remains  of  species  of 
shells  still  living  greatly  predominate,  and  the  presence  of  absolutely  extinct 
species  becomes  the  exception.* 

306.  'In  view  of  these  facts,  and  taking  the  percentage 
of  living  species  of  shells  found  fossil  in  different  parts 
of  the  system  as  their  guide,  geologists  have  divided  the 
Tertiary  strata  into  four  groups  ;  which,  commencing 
with  the  oldest  and  ascending  in  the  series,  have  been 
designated  as  follows  :  1.  EOCENE  ;  2.  MIOCENE  ;  3.  PLIO- 
CENE ;  4.  PLEISTOCENE. 

Each  of  these  names,  by  its  signification,  is  intended  to  express  the  paleon- 
tological  character  of  the  group  to  which  it  applied.  Thus — 

Eocene  (G-r.,  f/wf,  dawn ;  and  Kat,vo£,  recent)  implies  the  dawn,  or  com- 
mencement of  existing  things — about  five  per  cent,  of  the  shells  found  in  the 
strata  of  this  group  being  identical  with  living  species.f 

Miocene  (Gr.,  fj.£iuv,  less)  implies  that  the  proportion  of  living  species  is 
still  less  than  that  of  the  extinct — about  twenty-five  per  cent,  of  the  shells 
found  fossil  in  this  group  being  identical  with  living  species. 

QTJT.BTIOXS. — Where,  in  the  geological  series,  do  we  first  find  fossils  which  are  regarded 
as  identical  with  living  species  ?  In  what  manner  have  the  strata  of  the  Tertiary  system 
been  divided  ?  What  is  the  signification  of  the  names  applied  to  groups  of  the  Tertiary  ? 


*  "  Whoever  examines  a  museum  containing  a  pretty  complete  collection  of  organic  re- 
mains, arranged  in  chronological  order,  cannot  fail  of  being  struck  with  the  following 
facts :  When  looking  over  the  Palaeozoic  fossils,  the  forma  will  all  appear  so  strange 
to  him,  that  lie  will  hardly  be  able  to  pronounce  to  which  class  of  the  animal  king- 
dom some  of  them  belong.  Even  where  the  class  is  evident,  as  for  instance  with 
the  shells,  he  will  see  that  they  obviously  differ  from  existing  shells.  There  are  no 
oysters,  or  barnacles,  or  cockles,  or  limpets  among  them.  The  more  familiar  the  observer 
may  be  with  our  present  kinds,  the  more  strange  the  ancient  specimens  will  appear. 
When  he  proceeds  to  the  shells  of  the  Mesozoic  period  they  will  seem  much  more  familiar 
to  him.  He  will  say  of  one,  perhaps,  '  This  is  like  an  oyster,'  or  '  a  Venus  (clam) ;'  or,  of 
another,  'This  resembles  a  trochus;'  still,  if  he  be  well  acquainted  with  recent  shells, 
he  will  not  be  able  to  discover  a  single  specimen  to  which  he  can  assign  not  only  a 
generic  but  a  specific  name.  He  will  not  be  able  to  say,  '  This  is  such  and  such  a  Venus, 
or  trochus,  of  the  same  species  as  one  that  I  have  in  my  cabinet  of  recent  shells  at  home.' 
When,  however,  he  comes  to  the  fossils  got  from  tertiary  rocks,  it  is  no  longer  the  differ- 
ence between  the  fossil  and  the  living  forms  that  will  strike  him,  but  their  resemblance, 
and,  in  some  cases,  their  identity.  The  curious,  old  puzzling  forms  have  all  disappeared ; 
almost  every  species  belongs  to  a  still  existing  genus,  or  is  very  closely  allied  to  it ; 
oysters  and  barnacles,  cockles,  limpets,  and  numerous  other  kinds  now  appear  in  great 
abundance,  and  in  many  varieties.  We  have,  therefore,  in  these  facts,  most  obvious 
expression  of  a  great  law,  that,  namely,  of  the  gradual  approximation  to  existing  forms, 
and  the  gradual  appearance  of  existing  species.  The  first  may  be  traced  throughout  the 
series  of  life,  from  the  earliest- to  the  latest  times;  the  last,  which  is  its  necessary  con- 
clusion, is  only  apparent  in  the  Tertiary  epoch." — London  Quarterly  Review. 

t  Some  eminent  naturalists,  among  whom  we  may  include  Professor  Agassiz,  are  of 
the  opinion  that  while  fossil  and  living  species  are  often  closely  related,  and  apparently 
the  same,  yet  we  cannot  in  any  case  prove  complete  identity. 


280      FIRST     PRINCIPLES     OF     GEOLOGY. 

Pliocene  (Gr.,  7r/,«6n;,  more)  implies  that  the  proportion  of  living  species 
is  more  or  greater  than  that  of  extinct — the  number  of  living  forms  among 
the  fossil  shells  of  this  group  ranging  from  fifty  to  seventy  per  cent 

Pleistocene  (G-r.,  Tcfaiaros,  most)  implies  a  majority;  and  in  this  group  the 
shells  found  fossil  are  mostly  those  of  species  inhabiting  the  present  seas. 

«. 

307.  Eocene,    Miocene,    and    Pliocene    Groups, — These 
three  groups  (which,  according  to  the  classification  adopted 
by  some  geologists,  are  made  to  comprise  the  whole  of  the 
Tertiary  system)  resemble  one  another  so  closely  in  their 
lithological  characters  that  it  is  almost  impossible  to  draw 
any  distinct  line  of  separation  between  them,  or  to  identify 
them,  except  by  a  comparison  of  their  inclosed  fossils  with 
living  species.      "They  should,  in  fact,  be  regarded  as 
the  successive  steps  or  stages  of  one  great  and  undisturbed 
formation." 

Composition, — The  deposits  referable  to  these  groups,  are,  on  the 
whole,  much  less  consolidated  than  the  strata  of  the  older  systems ;  and 
consist,  for  the  most  part,  of  variously  colored  sands  and  clays,  with  inter- 
stratified  limestones,  gypsums,  siliceous  sandstones,  marls,  and,  not  unfrc- 
quently,  beds  of  lignite. 

308.  Geographical    Distribution, — As  far  as  discovery  has  gone, 
there  are  few  countries  in  which  Eocene,  Miocene,  or  Pliocene  Tertiary  strata 
have  not  been  detected.     In  Europe  and  Asia  they  occupy  well-defined 


1.  Kiver  Thames. 


2.  London. 


3.  Marine  Sands. 


tracts  or  basins,  and  appear  to  havo  been  deposited  in  inland  seas  or  estua- 
ries of  limited  extent.  In  some  instances  the  strata  are  strictly  marine,  and 
in  others  as  decidedly  fresh  water ;  while  in  many  of  the  Tertiary  basins  of 
Europe  they  are  partly  fresh  water  and  partly  marine,  "  as  if  there  had  been 
frequent  submergences  and  elevations,  or,  at  all  events,  periods  when  fresh 
water  inundations  prevailed  over  the  areas  of  deposit."  The  cities  of  London, 


QUESTIONS. — What  Is  said  of  the  lithological  character  of  the  Eocene,  Miocene,  and 
Pliocene  Tertiaries?  What  of  their  composition  ?  "What  of  their  geographical  distribu- 
tion in  the  Old  World  ? 


CAINOZOIC     PERIOD.  281 

Paris,  and  Vienna  are  each  situated  upon  a  Tertiary  basin.  Fig.  181  repre- 
sents a  section  of  the  London  basin,  which  lies  in  a  trough  or  hollow  of  the 
Cretaceous  system. 

In  North  America,  Tertiary  deposits  of  the  groups  of  the  Eocene,  Miocene, 
or  Pliocene  occur  along  the  Atlantic  coast,  from  Massachusetts  to  Mexico, 
and  include  the  whole  of  Florida  and  large  areas  of  the  States  of  Alabama, 
Mississippi, 'Louisiana,  Texas,  and  Arkansas.  They  are  also  found  upon  the 
Pacific  coast,  from  Lower  California  to  Russian  America ;  and  in  the  interior 
of  the  Continent,  upon  the  eastern  slope  of  the  Rocky  Mountains,  in  the 
region  of  the  head-waters  of  the  Missouri — Kansas  and  Nebraska — they 
cover  an  immense  extent  of  surface.  Upon  the  Atlantic  coast,  south  of 
Delaware,  the  western  limit  of  these  Tertiary  deposits  is  at  the  first  or  lowest 
falls  of  the  principal  rivers,  and  is  generally  marked  by  the  long-leaved  pine 
(Pinus  palustris),  whose  distance  from  the  shore  is  said  to  be  limited  by  these 
formations. 

309.  Life  of  the  Epochs  represented  by  the  Eocene, 
Miocene,  and  Pliocene  Tertiaries, 

Plants , — The  vegetation  of  the  earth  during  the  earlier  ages  of  the 
Tertiary  must  have  presented  an  aspect  widely  different  from  that  of  any 
former  era.  The  tree-ferns,  the  cycadaceae,  and  the  allied  plants,  so  abundant 
in  the  Mesozoic  period,  sink  into  their  present  proportions;  while  true  exo- 
genous trees  and  shrubs,  which  had  previously  few  or  no  representatives  in 
nature,  became  largely  developed. 

During  the  epoch  of  the  Eocene  the  vegetation  appears  to  have  been  of  a 
tropical  or  semi-tropical  character,  and  belonged,  for  the  most  part,  to  species 
which  are  now  extinct.  In  the  latitude  of  London  there  were,  undoubtedly, 
forests  of  palms ;  inasmuch  as  from  the  strata  of  Eocene  clays,  upon  which 
the  city  of  London  is  built,  the  fruits  of  no  less  than  thirteen  different  species 
of  this  family  are  obtainable. 

In  the  Middle  or  Miocene  Tertiary  the  fossil  vegetation  partakes,  perhaps, 
in  a  nearly  equal  degree,  of  a  temperate  and  tropical  character  but  as  we 
rise  in  the  series  the  temperate  forms  predominate;  and  in  the  Pliocene 
strata  the  vegetation  closely  resembles  that  which  is  now  found  in  the 
temperate  regions  of  North  America,  Europe,  and  Japan.  In  the  United 
States,  however,  a  large  number  of  fruits  and  seeds  of  apparently  tropical 
character  have  been  obtained  from  a  deposit  of  lignite  of  Upper  Tertiary  age, 
occurring  as  far  north  as  Brandon,  in  the  State  of  Vermont.* 

QUESTIONS. — What  of  their  distribution  in  North  America  ?  "What  is  said  of  the  vege- 
tation of  the  earth  during  the  earlier  ages  of  the  Tertiary  ?  "What  is  known  of  the  vege- 
tation of  the  Eocene  epoch  ?  What  of  the  Miocene  and  Pliocene  epochs  ?  Is  there  any 
evidence  of  the  former  existence  of  a  tropical  vegetation  in  New  England? 


*  So  far  as  we  can  judge,  says  Hugh  Miller,  neither  flock  nor  herd  could  have  found 
support  on  the  greenest  and  richest  plains  of  the  lands  of  the  Carboniferous  epoch  or  of 
the  Oolite ;  and  it  is  not  until  we  enter  on  the  Tertiary  ages  that  we  find  floras  amid 
which  a  man  might  have  profitably  labored  as  a  dresser  of  gardens,  a  tiller  of  fields,  or  a 


282       FIRST     PRINCIPLES     OF     GEOLOGY. 

310.  Amber  ,  —  One  of  the  most  curious  products  of  the  Tertiary  system  is 
the  substance  termed  amber  /  which  is  now  known  to  bo  the  fossil  resin  of 
an  extinct  species  of  pine.  It  is  usually  found  in  beds  of  tertiary  clays  and 
sands,  and  is  often  associated  with  the  wood  of  the  trees  from  which  it  was 
exuded  —  the  wood  being  in  a  state  of  lignite,  and  sometimes  having  the 
amber  adherent  to  it.  The  most  abundant  source  of  supply  of  amber  is  a 
Tertiary  formation  on  the  Prussian  coast  of  the  Baltic  Sea,  where  the  amber  is 
obtained  by  digging  and  mining,  and  is  also  found  in  datached  masses  upon 
the  sea  shore,  where  it  is  washed  up  by  the  waves  from  Tertiary  strata  be- 
neath the  ocean.  As  much  as  800  pounds  have  been  thus  thrown  up  on 
the  Baltic  coast  during  a  single  storm.  Amber  also  occurs  in  the  Tertiary 
clays  of  Great  Britain,  and  fine  specimens  are  not  unfrequently  found  while 
excavating  beneath  the  city  of  London.  In  the  United  States  it  has  been 
found  at  various  localities  (though  not  in  large  quantities)  ;  as  at  Amboy, 
New  Jersey;  Gay  Head,  on  Martha's  Vineyard;  and  at  Cape  Sable,  in 
Maryland.  The  largest  specimen  of  amber  known  weighs  eighteen  pounds. 
and  is  preserved  in  the  Eoyal  Museum  of  Berlin.* 

But  apart  from  the  circumstances  of  its  origin  and  occurrence,  amber  has, 
for  the  geologist,  a  peculiar  interest,  inasmuch  as  it  forms  the  best  of  all 
materials  for  the  preservation  of  the  most  delicate  organisms  of  the  Tertiary 
ages.  Mosses,  fungi,  and  liverworts  are  plants  of  so  delicate  a  structure 
that  they  are  rarely  or  never  preserved  in  shale  or  stone  ;  but  specimens  of 
all  three  have  been  found  locked  up  in  amber,  in  a  state  of  the  most  perfect 
keeping.  And,  besides  containing  fragments  of  the  pine  which  produced  it, 
amber  has  been  found  to  contain  minute  pieces  of  four  other  species  of  pine,. 
with  bits  of  cypresses,  oaks,  poplars,  beeches,  etc.,  in  all  forty-eight  different 
species  of  shrubs  and  trees,  which  must  have  flourished  in  the  forests  where 
it  was  exuded,  and  which,  "  viewed  in  a  group,  may  bo  regarded  as  con- 
stituting," says  Prof.  Goeppert,  "a  flora  of  North  American  character." 

The  most  remarkable  organisms  of  amber  are,  however,  its  fossil  insects, 
which,  originally  enveloped  in  the  resin  as  it  flowed  in  a  liquid  state  from  the 
tree,  have  been  preserved  in  a  condition  of  perfect  entireness.  In  the  amber  of 
Prussia  alone,  upward  of  800  different  kinds  of  insects  have  been  determined, 


.—  What  curious  product  is  found  in  the  Tertiary  system?  What  is  amber? 
Under  what  circumstances,  and  where  is  it  found  ?  What  circumstances  render  amber 
particularly  interesting  to  geologists  ?  What  is  said  of  the  organisms  inclosed  in  it  ? 

keeper  of  flocks  or  herds.  Furthermore,  there  are  -whole  orders  and  families  of  plants 
of  the  very  first  importance  to  man,  which  do  not  appear  until  late  in  even  the  Tertiary 
system.  According  to  Agassiz,  the  order  of  Rosacese  —  an  order  to  which  the  apple,  tlic 
pear,  the  peach,  the  raspberry,  the  strawberry,  the  almond,  and  most  cultivated  fruits 
belong,  together  with  all  the  species  of  roses  —  was  introduced  only  a  short  time  previous 
to  the  appearance  of  man  upon  the  earth.  "  And  the  true  grasses—  a  still  more  import- 
ant order,  which,  as  the  cereal  plants  of  the  agriculturist,  feed  at  the  present  time  at 
least  two  thirds  of  the  human  species,  and  in  other  humbler  varieties  form  the  staple 
food  of  the  grazing  animals  —  scarce  appear  in  the  fossil  state  at  all.  They  are  peculiarly 
plants  of  the  human  period.'1 

*  The  value  of  amber  depends  much  upon  the  size  and  purity  of  the  specimen.  Pieces 
of  ten  or  twelve  pounds  weight  command  several  thousands  of  dollars  ;  while  a  piece  of 
a  pound  weight  may  not  sell  for  more  than  fifty  dollars. 


CAINOZOIO      PERIOD.  283 

most  of  them  belonging  to.  species  and  even  genera,  that  appear  to  be  dis- 
tinct from  any  now  known ;  while  of  the  others,  some  are  nearly  related  to 
European  species,  and  some  seem  identical  with  living  forms  that  inhabit 
the  tropics.  Among  these  insects,  the  first  fossil  bee  is  found,  associated 
with  moths  and  butterflies ;  a  fact  which  proves  the  contemporary  existence 
of  flower-bearing  herbs  and  trees. 

311.  Animals, — The  fossil  invertebrate  animals  of  the 
Eocene,  Miocene,  and  Pliocene  groups — infusoria,  corals, 
star-fishes,  molluscs,  Crustacea,  insects,  etc. — are  extremely 
abundant,  both  numerically  and  in  point  of  species. 

In  this  country,  deposits,  composed  almost  entirely  of  the  siliceous  cover- 
ings of  infusorial  organisms,  constitute  no  inconsiderable  part  of  the  Eocene 
and  Miocene  Tertiary  strata  of  Maryland  and  Virginia — some  of  the  beds  of 
infusorial  earth  near  Richmond,  Va.,  being  from  twenty  to  fifty  feet  in  thick- 
ness. (See  §  68,  Fig.  21.) 

In  the  Old  "World  the  most  important  member  of  the  Tertiary  system  is  a 
formation  of  limestone,  of  the  group  of  the  Eocene,  which  is  almost  wholly 
made  up  of  a  class  of  fossil  foramini- 
ferous  shells,  of  the  size  and  appear- 
ance of  a  small  coin;  and  hence 
termed  mimmulites,  from  Latin,  num- 
mus,  a  coin  (see  Fig.  188).  In  the 
Alps  of  Switzerland  this  nummulitic 
limestone  attains  a  thickness  of  several 
thousand  feet,  and  from  thenco  it 
may  be  traced  at  intervals  through- 
out Southern  Europe,  and  Northern 
Africa  into  Asia,  as  far  as  the  Hima- 
laya Mountains,  where  extensive  beds  of  it  have  been  recognized  at  an  ele- 
vation of  16,500  feet  above  the  level  of  the  sea.  It  was  also  largely  quarried 
in  Egypt  for  the  construction  of  the  Pyramids  and  the  Sphinx,  and  the  curi- 
ous organisms  that  compose  it  have  received  from  the  Arabs  the  name  of 
"  Pharaoh's  beans."* 

QUESTIONS. — What  is  said  of  the  fossil  invertebrate  animals  found  in  the  Eocene, 
Miocene,  and  Pliocene  Tertiaries  ?  What  of  the  infusorial  deposits  of  this  country  f 
What  is  the  most  important  of  the  Tertiary  deposits  of  the  Old  World  ?  What  is  said 
of  the  distribution  of  the  nummulitic  limestones  ? 


*  The  use  of  this  limestone  in  the  construction  of  the  Pyramids  illustrates  tho  fact, 
that  "  some  of  the  oldest  things  in  the  world,  in  their  relation  to  human  history — erec- 
tions, many  of  which  had  survived  the  memory  of  their  founders,  even  in  the  days  of 
Herodotus — are  formed  of  materials  so  modern  in  their  relation  to  the  geological  epochs, 
that  they  had  no  existence  as  rock  until  after  the  Palaeozoic  and  Mesozoic  ages  had  gone 
by."  Not  only  the  "  Quincy  granites"  and  "  Berkshire  marbles"  of  New  England,  but 
even  the  red  and  buff  sandstones  so  extensively  quarried  in  the  Valley  of  the  Connecticut 
River,  in  New  Jersey,  and  Nova  Scotia,  are  of  an  antiquity  incalculably  vast  compared 
with  the  stone  out  of  which  the  oldest  of  the  Pyramids  was  bui?t 


284         FIBST     PRINCIPLES     OF     GEOLOGY. 

Another  peculiar  formation  of  the  European  Eocene  is  the  so-called  "  in- 
dusial  limestone"  a  name  given  to  a  series  of  fresh  water  strata  found  in  Cen- 
tral France,  which  are  almost  wholly  composed  of  the  cases,  or  "indusiae," 
of  the  caddis- worms  (the  larvce  of  a  species  of  fly).  Great  heaps  of  these  cases 
have  been  incrusted  with  carbonate  of  lime,  and  have  thus  consolidated  into 
a  species  of  limestone. 

In  the  Eocene  deposits  of  the  United  States,  east  of  the  Mississippi,  only 
marine  fossils  have  been  found ;  but  somo  idea-  of  their  abundance  may  be 
derived  from  the  fact,  that  a  formation  of  the  older  Eocene,  occurring  at 
Clairborne,  Alabama,  has  alone  yielded  more  than  400  distinct  species  of 
marine  shells,  echinoderms,  and  fishes.  Upon  the  Ashley  and  Cooper  Rivers, 
near  Charleston,  S.  C.,  beds  of  Eocene  clays  are  also  exposed  in  many  locali- 
ties, which  are  so  crowded  with  marine  fossils  that  a  person  seeing  them  for 
the  first  time  can  hardly  find  words  to  express  his  amazement  at  their  num- 
ber and  perfect  preservation.  The  majority  of  these  fossils,  however,  belong 
to  extinct  species. 

The  Miocene  beds  of  the  Southern  Atlantic  States  have  thus  far  furnished 
about  200  species  of  marine  fossils;  and  of  these,  about  twenty  per  cent,  of 
the  shells  and  corals  are  regarded  as  identical  with  living  species. 

It  has,  however,  been  remarked,  that  of  all  the  numerous  organic  remains 
contained  in  the  Eocene  and  Miocene  deposits  of  the  Atlantic  States,  only 
two  or  three  species  in  a  hundred  are  common  to  both  groups — a  fact  which 
indicates  that  a  considerable  period  of  time  elapsed  between  the  completion 
of  the  one  and  the  commencement  of  the  other,  during  which  no  strata  were 
deposited  in  this  region. 

312.  Fishes  , — The  number  of  fossil  fishes  found  in  the  Eocene,  Miocene, 
and  Pliocene  groups  is  very  large — 188  genera,  embracing  several  hundred 
species,  having  been  described. 

One  of  the  most  celebrated  localities  of  fossil  fish  known,  occurs  in  a  deposit 
of  Eocene  limestone  at  Mt.  Bolca,  in  Northern  Italy.  Here,  within  a  limited 
area,  the  rock  contains  thousands  upon  thousands  of  specimens  in  a  most  re- 
markable state  of  preservation.  The  fish  are  all  compressed  flat,  but  the 
scales,  bones,  and  fins  remain ;  their  color  (a  deep  brown)  contrasting  ad- 
mirably with  the  light-colored  limestone  in  which  they  aro  embedded.  The 
presence  of  such  immense  numbers  in  one  locality  is  explained  on  the  sup- 
position that  the  limestone  in  which  they  are  inclosed  was  erupted  into  the 
ocean  in  a  state  of  mud,  by  volcanic  agency,  and  that  the  fishes  were  at  once 
suffocated,  and  surrounded  by  the  calcareous  mass.  Some  idea  of  the  per- 
fection of  these  fossils  may  be  formed  from  Fig.  189,  which  represents  a 
specimen  from  this  locality. 

QUESTIONS. — "What  is  the  "indusial"  limestone?  What  is  said  of  the  Eocene  fossils 
of  the  United  States  ?  What  of  Miocene  ?  Is  it  probable  that  any  great  interval  of  time 
elapsed  between  the  deposition  of  these  two  groups  of  strata  ?  What  is  said  of  the  fossil 
fish  of  the  Tertiary  eystem  ?  What  locality  is  particularly  celebrated  for  these  fossils  ? 


CAINOZOIC      PERIOD.  285 

FJG.  189. 


Fig.  190  represents  a  slab  of  Tertiary  marl,  from  Central  Franco,  which 
contains  a  multitude  of  small  fishes,  as  perfect  as  if  recently  enveloped  in 
soft  mud.  , 

FIG.  190. 


The  Squalidse,  or  Shark  family,  have  had  representative  species  in  the 
oceans  of  every  geological  epoch  since  the  first  creation  of  fishes ;  but  in  the 
seas  of  the  Eocene  and  Miocene  this  family  appears  to  have  flourished  in 
great  numbers ;  and,  in  the  Eocene  and  Miocene  strata,  along  the  Atlantic 
coast  of  the  United  States,  the  teeth  of  sharks  are  among  the  most  common 
of  marine  fossils.  Some  of  these  teeth  are  of  immense  size,  and  must  have 

QUESTION.— What  class  of  fishes  Were  especially  numerous  in  the  seas  of  the  Eocene 
and  Miocene? 


286       FIRST     PRINCIPLES     OF     GEOLOGY. 

belonged  to  sharks  much  larger  than  any  living  species.  One  of  the  largest 
sharks  of  the  present  ocean  (thirty-seven  feet  long),  described  by  Prof.  Owen, 
had  teeth  two  inches  long,  and  nearly  two  broad ;  but  fossil  sharks'  teeth 
have  been  found  in  the  Atlantic  Tertiaries  which  measure  five  to  six  inches 
in  height  by  five  inches  in  width,  at  the  base.  "If,"  says  Prof.  Owen,  "the 
proportion  of  these  extinct  sharks  corresponded  with  those  of  existing  species, 
they  must  have  equaled  the  great  whales  in  size  (i.  e.,  100  feet  in  length) ; 
and  combining,  with  the  organization  of  the  shark,  its  bold  and  insatiable 
character,  they  must  have  constituted  the  most  terrific  and  irresistible  of  the 
predaceous  monsters  of  the  deep." 

FIG.  -19]. 


Fig.  191  represents  specimens  of  these  fossil  teeth  of  sharks.  In  most 
cases  their  structure,  and  the  serratures  along  their  edges,  are  as  perfect  as 
are  the  teeth  of  existing  sharks.* 


QUESTION.— What  is  said  of  the  teeth  of  sharks  found  fossil? 


*  The  teeth  of  sharks,  both  fossil  and  existing  species,  all  possess  one  essential  charac- 
ter of  structure,  namely,  a  base,  or  osseous  root,  of  variable  form,  which  is  implanted  in 
the  integuments ;  and  a  crown,  or  external  portion,  which  projects  into  the  mouth  and 
is  covered  with  enamel.  These  teeth  are  never  embedded  in  sockets,  or  united  to  the 
solid  margin  of  the  jaws;  they  only  adhere  to  the  integuments  of  the  mouth,  and  possess, 


CAINOZOIC       PERIOD.  287 

313.  Reptiles, — The  remains  of  reptiles  are  abundant  in 
the  deposits  of  the  Tertiary  epoch,  bat  are  not  so  numer- 
ous, comparatively,  as  in  the  rocks  of  the  Mesozoic  period. 

Of  crocodiles,  eighteen  species  have  been  described  from  Tertiary  strata 
— those  found  fossil  in  the  Eocene  clay,  which  underlies  the  city  of  London, 
being  closely  allied  to  the  crocodiles  which  are  now  living  on  the  Island  of 
Borneo.  Turtles  were  especially  numerous  during  the  Tertiary  epoch,  and 
not  unfrequently  attained  to  great  size — the  remains  of  one  individual,  found 
in  Tertiary  strata,  at  the  base  of  the  Himalaya  Mountains,  measuring  twenty 
feet  across  the  curve  of  the  shell.  The  earliest  indications  which  the  pale- 
ontologist obtains  of  the  existence  of  Ophidians,  or  serpents,  upon  the  surface 
of  our  planet  occur  also  in  the  Tertiary,  where,  at  least,  ten  species  of  this 
family  have  been  found  fossil.  Some  of  these  were,  apparently,  allied  to  the 
boa,  or  anaconda,  while  others  were,  undoubtedly,  sea  snakes,  and  judging 
from  the  corresponding  parts  of  recent  species,  they  must  have  been  from 
fourteen  to  twenty  feet  in  length. 

314.  Mammalia, — But   the  most   remarkable   and  in- 
teresting of  all  the  fossil  remains  found  in  the  deposits  of 
the  Tertiary  system  are  those  of  Mammalia.     As  already 
stated,  the  remains  of  mammiferous  animals  first  appear 
in  the  Triassic  system  ;    but   during  the  whole  of  the 
Mesozoic  period  this  great  division  of  the  animal  kingdom 
seems  to  have  been  represented  on  the  surface  of  our  planet 
by  only  a  few  species  belonging  to  its  lowest  and  most 
inferior  orders, — as  the  marsupalia,   etc.     With  the  very 
commencement  of  the  Tertiary  epoch,  however,  mammalia 
appear  to  have  been  called  into  existence  in  great  num- 
bers, and  from  this  time  onward,  to  the  present,  they  con- 
stitute the  predominant  races,  so  much  so,  that  the  Cai- 
nozoic  period  is  sometimes  designated  as  the  "  reign  of 
mammals^'  in  the  same  manner  as  the  Mesozoic  period  is 
termed  the  "*reign  of  reptiles/'  and  the  Palaeozoic  period 
the  "  reign  offisJies." 

QUESTIONS. — What  is  said  of  the  reptilian  life  of  the  Tertiary  epoch?  What  varieties 
of  reptiles  appear  for  the  first  time  in  the  Tertiary  ?  What  are  the  most  remarkable 
fossils  yielded  by  this  system  ?  What  is  said  of  the  development  of  mammalian  life  on 
the  earth  during  the  Tertiary  ages?  What  designation  characteristic  of  its  life  features 
is  sometimes  given  to  the  Cainozoic  period  ? 

in  most  of  the  sharks,  great  mobility.  They  are  generally,  moreover,  disposed  in  rows ; 
the  anterior  ones,  being  first  used,  fall  out,  and  are  replaced  by  those  on  the  inner  series. 
New  teeth  are  also  continually  formed  behind  those  which  exist,  and  advance  successively 
toward  the  anterior  rows  as  the  latter  are  shed,  and  ia  their  turn  occupy  the  first  rank. 


288       FIRST     PRINCIPLES     OF     GEOLOGY. 

The  Eocene  ages  were  especially  characterized  by  the  existence  of  large 
numbers  of  animals  of  the  order  Pachydermata  (G-r.,  na^vc,  thick;  (Jep/za, 
skin),  an.  order  of  mammals  which  have  hoofs,  but  do  not  chew  the  cud,  and 
which  are  distinguished  for  the  thickness  of  their  skins — as  the  elephant, 
rhinoceros,  hippopotamus,  tapir,  hog,  horse,  etc.  The  Pachydermata  of  the 
Eocene  period  were,  however,  so  different  from  any  now  existing,  that  new 
generic  names  have  had  to  be  invented  for  almost  all  of  them. 

One  variety  of  Pachydermatous  animal,  of  which  eleven  or  twelve  species 
have  been  found — varying  in  size  from  that  of  a  horse  to  that  of  a  hog  or 
sheep — had,  in  its  skeleton,  the  united  characteristics  of  the  tapir,  the  rhi- 
noceros, and  the  horse.  It  is  named  Palceotherium  (Gr.,  rcahqioc.,  ancient; 
and  drjpiov,  wild  beast),  and  was  furnished  with  a  short  fleshy  trunk,  which 
probably  adapted  it  to  live  like  the  South  American  tapir,  in  swampy  dis- 
tricts, and  feed  on  coarse  vegetation.  Fig.  102,  page  186,  will  give  some 
idea  of  its  appearance  and  structure. 

Another  genus,  of  which  five  species  have  been  found,  was,  in  one  respect, 
intermediate  between  the  rhinoceros  and  the  horse,  and  in  another  between 
the  hippopotamus,  the  hog,  and  the  camel.  It  was  especially  distinguished  by 
the  great  length  of  its  tail,  which  was  longer  than  its  body.  This  animal  has 
received  the  namo  of  Anoplotherium  (avoTr/lof,  unarmed),  and  varied  in  size 
from  the  dimensions  of  a  pony  to  that  of  a  hare.  (See  Fig.  192.) 

FIG.  192. 


Besides  mammals  of  the  order  Pachydermata,  there  have  also  been  found 
in  the  Eocene  Tertiaries  the  fossil  remains  of  the  dog,  hyena,  fox,  opossum, 
squirrel,  monkey,  and  bat — all  of  extinct  species ;  also  the  bones  of  many 
species  of  birds. 

The  most  interesting  collection,  probably,  of  the  remains  of  the  animals  of 
the  Eocene  has  been  obtained  from  certain  beds  of  gypsum,  which  form  a  part 
of  the  Tertiary  basin  in  which  the  city  of  Paris  is  situated.  In  this  formation 

QUESTIONS.— What  class  of  animals  especially  flourished  during  the  age  of  the  Eocene  ? 
"What  are  the  peculiarities  of  the  Pachydermata  ?  What  were  some  of  the  most  remark- 
able Eocene  quadrupeds  ?  What  locality  has  furnished  the  most  interesting  fossils  of 
the  Eocene? 


CAINOZOIC      PERIOD. 


289 


the  remains  of  upwards  of  fifty  species  of  quad- 
rupeds have  been  found,  four-fifths  of  which  are 
referable  to  the  order  of  the  Pachydermata.  Tho 
beds  also  contain  land  and  fresh  water  shells, 
fragments  of  wood,  with  numerous  bones  of 
fresh  water  fish,  reptiles,  and  birds.  The  skele- 
tons of  the  quadrupeds  usually  occur  isolated, 
and  are  often  in  such  a  peculiar  and  partial  state 
of  preservation  as  "  to  excite  the  curiosity  of 
even  the  untaught  workmen.  Only  half  the ' 
skeleton  is  present.  The  limbs  and  ribs  of  the 
under  side  are  found  lying  in  nearly  their  proper 
places;  while  of  the  limbs  and  ribs  of  the  upper 
side  usually  not  a  trace  can  be  detected;  even 
the  upper  side  of  the  skull  is  often  wanting.  It 
would  almost  seem  as  if  somo  pro-Adamite 
butcher  had  divided  the  carcass  longitudinally, 
and  carried  away  with  him  all  the  upper  halves. 
The  reading  of  the  enigma  seems  to  be,  that 
when  the  creatures  lay  down  and  died,  the 
gypsum,  in  which  their  remains  occur,  was  soft 
enough  to  permit  their  under  sides  to  sink  into 
it,  and  that  then  gradually  hardening,  it  kept 
the  bones  in  their  places ;  while  the  uncovered 
upper  sides,  exposed  to  disintegrating  influences, 
either  mouldered  away  piecemeal  or  were  re- 
moved by  accident." 

In  the  Eocene  beds  of  the  United  States,  east 
of  the  Mississippi,  the  remains  of  no  terrestrial 
mammalia  or  land  quadrupeds  have  as  yet  been 
discovered,  but  vestiges  of  Cetacean  mammalia* 
are  not  uncommon.  In  Clark  County,  Alabama, 
the  colossal  bones  of  an  animal  of  this  order, 
termed  the  "  Zeuglodon,"  are  of  common  occur- 
rence in  certain  calcareous  strata.  Mr.  Lyell 
speaks  of  the  vertebral  column  of  one  skeleton, 
more  than  seventy  feet  in  length,  at  one  locality 
which  he  visited,  and  of  another  fifty  feet  long. 
Fig.  193  represents  a  restored  appearance  of  the 
zeuglodon. 

315.  In  the  Miocene  Tertiary,  Pachydermata, 

QUESTIONS. — What  mammalian  fossils  have  heen 
found  in  the  Eocene  strata  of  the  United  States  east 
of  the  Mississippi  ? 

*  The  order  Cetacea  includes  the  -whales,  dolphins, 
seals,  porpoises,  and  other  warm-blooded  animals  in- 
habiting the  ocean. 


FlG.  193. 


290       FIKST     PRINCIPLES     OF     GEOLOGY. 

though  mainly  cf  a  different  type  from  their  predecessors,0  are  still  the 
prevailing  forms.  One  animal  of  this  kind,  called  the  Dinotherium  (Gr., 
det.vog,  terrible;  and  6qptov,  wild  beast),  is  supposed  to  be  the  largest  mam- 
malian quadruped  that  ever  existed.  It  seems  to  have  been  a  kind  of  great 
water  elephant,  with  a  length  of  at  least  eighteen  feet,  and  a  height  of  four- 
teen feet;  two  feet  longer  and  higher  than  the  largest  mastodon  yet  dis- 
covered. It  was  probably  furnished  with  a  trunk  or  proboscis,  and  the  lower 
jaw  had  two  immense  tusks,  curving  downward,  like  those  of  the  walrus, 
and  which,  in  some  specimens,  were  three  feet  in  length.  Its  fore  feet  were 
very  long,  and  a  mole-like  form  of  the  shoulder-blade  adapted  them  for  dig- 
ging. This  animal  is  believed  to  have  lived  principally  ia  the  water,  like  the 
hippopotamus,  and  probably  used  its  tusks  for  tearing  up  the  roots  of  aquatic 
plants,  which  the  structure  of  its  teeth  indicates  it  fed  upon.  It  has  also 
been  suggested  that  the  tusks  were  used  for  dragging  the  animal  out  of 
water,  or  for  anchoring  it  to  the  shore  while  it  slept  in  the  water.  Its 
head,  which  measured  about  three  feet  across,  was  provided  with  muscles 
of  enormous  strength,  arranged  so  as  to  give  the  most  potent  effect  to  the 
operations  of  the  tusks,  whatever  may  have  been  their  uses.  The  genus 
Dinotherium  appears  to  have  existed  but  for  a  limited  time ;  having  been 
created  at  the  commencement  of  the  Miocene  epoch  and  becoming  extinct  at 
its  close.  Its  remains  have  been  found  in  France,  Central  Europe,  Greece, 
India,  and  Australia.  Its  probable  appearance  is  represented  in  Fig.  194. 

FIG.  194. 


The  great  Mastodon  (Gr.,  [iaaroc,  nipple;  arid  utovc,  a  tooth),  an  animal 
resembling  the  elephant  (see  Fig.  208),.  and  deriving  its  name  from  the  pro- 
tuberances on  the  grinding  surfaces  of  its  teeth  (see  Fig.  195),  seems,  in 
Europe,  to  have  been  contemporary  with  the  Dinotherium ;  but  in  this  coun- 
try (the  scene  of  its  greatest  numerical  development)  it  appears  to  belong  to 
a  later  age.  In  height  it  did  not  surpass  the  African  elephant,  but  it  con- 
siderably exceeded  it  in  length — a  specimen  which  could  not  have  stood 
above  twelve  feet  high,  indicating  a  length  of  about  twenty-five  feet.  It  had 
tusks  like  the  elephant,  and  a  long,  flexible  proboscis. 

QUESTIONS. — What  is  said  of  the  animals  of  the  Miocene  epoch  ?  Describe  the  Dino- 
therium. What  animal  was  probably  contemporary  with  the  Dinotherium  in  Europe? 


*  Out  of  twenty  genera  of  mammalia  found  in  the  Eocene,  seventeen  have  never  been 
found  in  any  more  recent  deposits. 


CAINOZOIC      PERIOD.  291 

Another  curious  animal  of  this  era,  whose  remains  are  found  in  Tertiary 
deposits,  in  India,  was  the  "Sivatherium"  which  was  larger  than  a  rhino- 
ceros, and  furnished  with  four  horns,  and  a  proboscis.  When  living,  it  must 
have  resembled  an  immense  antelope  or  gnu,  with  the  face  and  figure  of  a 
rhinoceros.* 

FIG.  195.  FIG.  196. 


Fig.  195,  tooth  of  the  American  mastodon  ;  weight,  4  Iba.  ;— 

Fig.  196,  tooth  of  the  fossil  elephant,  or  mammoth  (one-sixth  of  the  diameter  of  the  original). 

316.  A  most  extraordinary  formation  of  the  age  of  the  Miocene  Tertiary 
has  been  brought  to  light  within  a  comparatively  few  years,  hi  Nebraska, 
in  the  district  of  country  known  as  the  " Mauvaises  Terres"  or  "Bad 
Lands,"  of  the  "White  Eiver.  Its  location  and  geological  features  are  thus 
described  by  Dr.  Owen,  IT.  S.  Geologist,  in  an  official  report  for  1851 : — 
"From  the  uniform  monotonous  open  prairie,  the  traveler  suddenly  descends 
one  or  two  hundred  feet,  into  an  extensive  valley  (about  thirty  miles  wide, 
by  ninety  in  length),  that  looks  as  if  it  had  sunk  avray  from  the  surrounding 
world,  leaving  standing,  all  over  it,  thousands  of  abrupt,  irregular  prismatic 
and  columnar  masses,  stretching  up  to  the  height  of  from  one  to  two  hundred 
feet,  or  more.  So  thickly  are  these  natural  towers  studded  over  the  surface 
of  this  extraordinary  region,  that  the  traveler  threads  his  way  through  deep, 
labyrinthine  passages,  not  unlike  the  narrow,  irregular  streets  of  some  quaint 
old  town ;  while  viewed  from  a  distance  one  might  almost  imagine  himself  ap- 
proaching some  magnificent  city  of  the  dead,  where  the  labor  of  forgotten 
millions  had  left  behind  them  a  multitude  of  monuments  of  art  and  skill." 


QUESTIONS.  —What  remarkable  animal  has  been  found  in  the  Tertiary  deposits  of 
India?    What  extraordinary  formation  of  the  Miocene  age  exists  in  this  country? 


*  The  Tertiary  deposit  from  which  the  remains  of  the  Sivatherium  are  obtained  lies 
at  the  southern  base  of  the  Himalaya  Mountains,  among  the  Sivalic  hills,  in  India,  and 
has  afforded  a  greater  number  of  genera,  and  species  of  fossil  mammalia,  than  any  other 
region  yet  explored  :  such  as  the  mastodon,  elephant,  hippopotamus,  giraffe,  camel,  mon- 
key, and  various  carnivorous  animals  allied  to  the  lion  and  tiger.  Casts  of  some  of  the 
most  interesting  of  these  fossils  have  been  presented  by  the  East  India  Company  to  the 
Boston  Society  of  Natural  History,  and  may  be  seen  in  their  museum. 


292       FIRST     PRINCIPLES     OF     GEOLOGY. 

"  On  descending  from  the  heights,  however,  and  proceeding  to  inspect  the 
deep,  intricate  recesses  of  this  vast  labyrinth,  the  realities  of  the  scene  soon 
dissipate  the  delusions  of  the  distance.  The  castellated  forms  which  fancy 
had  conjured  up  change ;  and  around  one,  on  every  side,  is  bleak  and  barren 
desolation." 

But  the  physical  features  of  the  Mauvaises  Terres  are  of  little  importance  in 
comparison  with  its  fossil  treasures.  The  region  seems  to  be,  in  fact,  one 
vast  charnel-house,  and  "at  every  step,"  says  Dr.  Owen,  "embedded  in  the 
debris,  lie  strewn,  in  the  greatest  profusion,  the  remains  of  extinct  animals." 

In  a  collection  of  from  six  to  eight  thousand  pounds  of  fossil  bones  brought 
from  this  locality,  Prof.  Leidy,  of  Philadelphia,  has  detected  the  remains  of 
about  thirty  species  of  extinct  mammalia.  Many  of  these  belonged  to  huge 
Pachydermatous  animals,  such  as  the  hippopotamus  (eight  species  of  which 
have  been  found),  rhinoceros,  tapir,  palseotherium,  anoplotherium,  etc.  One 
extinct  animal,  called  the  "  Oreodon"  had  grinding  teeth  like  the  elk  and 
deer,  and  also  sharp-pointed  teeth  like  lions,  cats,  etc. ;  and  must  have  be- 
longed to  a  race  that  lived  both  on  flesh  and  vegetables,  and  yet  chewed  the 
cud  like  the  cow.  Another,  called  the  Machairodus,  was  wholly  carnivo- 
rous, and  "combined  the  size  and  weight  of  the  grizzly  bear  with  the  jaws 
and  teeth  of  the  Bengal  tiger." 

Most  of  the  bones  are  in  a  relatively  good  state  of  preservation,  and  are 
highly  mineralized.  Dr.  Owen  saw  a  nearly  entire  skeleton  of  a  palseo- 
therium, which  measured,  as  it  lay  embedded,  eighteen  feet  in  length,  by 
nine  in  height;  also  a  jaw  of  a  similar  animal,  which  measured  five  feet  along 
the  range  of  its  teeth.  Besides  the  remains  of  mammalia,  fossil  turtles  are. 
numerous.  At  one  point  of  the  valley,  which  has  the  appearance  of  a  floor 
of  an  ancient  lake,  they  lie  embedded  by  the  hundreds;  and,  in  some  in- 
stances, have  an  estimated  weight  of  a  ton. 

All  the  fossils  thus  far  brought  from  the  Mauvaises  Terres  of  Nebraska 
are  believed  to  belong  to  species  that  became  extinct  before  the  epoch  when 
the  Mastodon  inhabited  this  country,  and  their  general  character  indicates 
that  the  strata  in  which  they  occur  embedded  was  deposited  from  fresh  or 
brackish  waters. 

311?.  Besides  the  fossil  animals  enumerated,  it  is  probable  that  every  exist- 
ing order  of  mammalia,  with  the  exception  of  man,  had  its  representatives 
upon  the  surface  of  our  planet  during  the  Tertiary  epoch. 

In  former  geological  epochs,  as  has  been  already  stated,  the  plants  and 
animals  of  every  region  of  the  globe  appear  to  have  presented  a  great  degree 
of  sameness  or  identity,  but  during  the  later  portions  of  the  Tertiary  epoch 
geographical  distinctions  and  separations  (life  provinces,  see  §  207)  began  to 
prevail.  Thus,  Australasia  is  now  the  exclusive  home  of  the  kangaroos, 
wombats,  and  all  other  existing  marsupalia,  with  the  exception  of  the  single 
genus  of  the  opossum;  and,  very  curiously,  the  bones  of  the  mammalia 

QUESTIONS Give  some  description  of  it  and  its  fossils.  What  proportion  of  the  exist- 
ing orders  of  mammalia  are  represented  in  the  later  Tertiary  deposits? 


CAINOZOIC      PERIOD.  293 

found  fossil  in  the  Tertiary  deposits  of  Australasia,  have  also  proved,  with 
very  few  exceptions,  to  be  those  of  marsupials.*  In  like  manner,  the  Ter- 
tiary fossil  mammalia  of  South  America  resemble  the  sloths,  armadillos,  ant- 
eaters,  and  other  animals  which  are  now  restricted  to  that  continent.  In 
New  Zealand,  before  the  arrival  of  Capt.  Cook's  ships,  no  mammal  existed 
larger  than  a  rat,  and  among  the  fossils  of  the  Tertiary  of  these  islands  a  like 
restriction  of  animal  forms  has  also  been  discovered  to  prevail.  Some  genera 
of  mammalia,  however,  have  always  had  a  much  wider  range  than  others, 
and  the  bones  of  the  mastodon  and  horse,  especially,  have  been  found  fossil 
in  the  Tertiary  deposits  of  almost  every  quarter  of  the  globe,  f 

318.  Pleistocene  Group , — In  the  present  state  of  geological  knowl- 
edge it  is  impossible  to  define  the  limits  of  this  most  recent  group  of  the 
Tertiary  system  with  precision,  but  upon  one  point  all  geologists  are  agreed, 
namely,  "that  while  the  Eocene,  Miocene,  and  Pliocene  strata  were  gradu- 
ally, and  during  a  long  series  of  ages,  deposited  in  seas,  estuaries,  and  lakes, 
surrounded  by  land  that  enjoyed  a  high  and  genial  climate,  some  immense 
changes — physically  and  geographically — took  place  over  these  areas,  which 
brought  the  Pliocene  to  a  close,  and  heralded  the  advent  of  the  Pleistocene 
era.  The  distribution  of  Pliocene  lands  and  seas  was  violently  broken  up,  the 
climate  was  changed,  and  the  huge  mammalia  that  browsed  in  thousands  in 
the  jungly  valleys,  or  roamed  over  the  wooded  plains,  met  with  a  rapid  and 
all  but  total  extinction." 

QTTESTIOXS. — What  remarkable  difference  is  manifest  on  comparing  the  fossils  of  the 
Tertiary  with  those  of  the  earlier  systems  ?  What  is  said  of  the  limits  of  the  Pleistocene 
group  ?  What  circumstances  appear  to  have  attended  the  advent  of  the  Pleistocene  era  ? 


*  Recent  geological  explorations  in  Australia  have  put  us  in  possession  of  many  inte- 
resting facts  respecting  the  animal  life  that  prevailed  on  this  great  island  continent  during 
the  Tertiary  epoch.  Nearly  all  the  principal  orders  of  terrestrial  mammalia  existing  in 
other  parts  of  the  globe  were  represented,  but  with  very  few  exceptions  they  were  all  mar- 
supials, or.pouched  animals.  Thus,  for  example,  there  was  a  large  carnivorous  quadru- 
ped, equaling,  probably,  the  largest  existing  lion  or  tiger  in  size  and  ferocity,  and  yefc 
was  a  pouched  animal  like  the  kangaroo  or  opossum.  It  was  contemporary  with,  and 
probably  preyed  upon,  kangaroos  four  or  five  times  larger  than  any  now  existing,  and 
also  upon  another  herbiverous  pouched  animal  (the  Diprodon),  which  had  a  head  and 
face  somewhat  like  a  kangaroo,  and  the  proportions  of  a  rhinoceros ;  the  size  of  the 
Diprodon  may  be  inferred  from  the  circumstance,  that  its  fossil  skull  measures  three 
feet  long,  by  one  foot  eight  inches  broad. 

t  At  the  time  of  the  discovery  of  the  American  continent  the  horse  was  unknown  to 
the  natives,  and  probably  did  not  then  exist  in  the  New  World — the  horses  now  found 
wild  in  North  and  South  America  being,  undoubtedly,  descendants  of  subsequent  Euro- 
pean importations.  Yet  the  bones  of  the  horse  are  found  fossil  in  the  very  latest  Tertiary 
deposits  of  the  United  States,  and  seem  to  warrant  the  inference  that  the  species,  after 
having  been  called  into  existence  upon  this  continent,  died  out,  and  was  then  renewed 
from  the  Old  "World  by  the  agency  of  man. 

According  to  Prof.  Owen,  no  unequivocal  fossil  remains  of  the  sheep  have  as  yet  been 
discovered ;  although  the  bones  of  the  goat  are  found  fossil  in  deposits  of  the  Pliocene 
and  Pleistocene  epochs.  The  inference  from  this  negative  evidence,  therefore,  is,  that 
the  sheep  is  not,  geologically,  more  ancient  than  man. 


294      FIRST     PRINCIPLES     OF     GEOLOGY. 

319.  Physical   Geography  of   the  Tertiary    Epoch, — Atthe 
commencement  of  the  Tertiary  epoch  many  of  the  most  extensive  mountain 
ranges  of  the  globe — as  the  Alps,  Pyrenees,  Carpathians,  Himalayas,  etc. — 
were  not  in  existence.     "We  know  this  from  the  circumstance,  that  strata  of 
unmistakably  Eocene  age,  filled  with  the  remains  of  marine  animals,  are  now 
found  high  up  on  their  flanks  or  summits.     (See  Fig.  15.)*    In  this  country, 
the  great  chain  of  the  Rocky  Mountains  had  also  not  attained  its  present 
elevation.     Sir  R.  I.  Murchison  considers  that  tho  Alps,  at  the  commence- 
ment of  the  Tertiary  epoch,  were  represented  by  merely  a  long  archipelago 
of  islands,  slightly  raised  above  the  surface  of  the  ocean. 

Some  of  the  other  marked  geographical  features  of  tho  globe,  during  the 
earlier  ages  of  the  Tertiary,  as  made  known  by  geological  investigations, 
were  as  follows:  The  Mediterranean,  or  another  great  and  corresponding 
inland  sea,  covered  the  deserts  of  Sahara,  Lower  Egypt,  and  a  part  of  Arabia, 
The  Straits  of  Gibraltar,  probably,  did  not  then  exist,  and  the  waters  of  the 
Mediterranean  mingled  through  the  channels  of  the  Red  Sea  and  the  Persian 
Gulf  with  the  Indian  Ocean.  Tho  islands  of  Great  Britain  were,  probably, 
connected  together,  and  also  with  the  continent,  the  English  Channel  not 
having  been  excavated.  The  North  Sea  and  the  Baltic  spread  over  the 
plains  of  Northern  Europe,  and  another  ocean  stretched  from  Siberia  and 
joined  with  the  Mediterranean  by  the  Black  Sea.  India  was  then  a  great 
triangular  island.  In  North  America,  the  Gulf  of  Mexico  covered  a  great 
part  of  the  territory  of  the  Gulf  States,  and  penetrated  into  the  interior  of  tho 
country,  as  far  as  the  head  waters  of  the  Missouri ;  while  a  deep  trough  or 
channel  of  ocean  water  divided  tho  continent  along  the  line  of  the  St.  Law- 
rence and  the  present  chain  of  the  great  lakes.  South  America  at  thte 
epoch  was,  probably,  represented  by  three  great  islands,  "the  Isthmus  of 
Panama  not  existing. 

During  the  whole  of  the  Tertiary  epoch  the  mountain  chains,  above  re- 
ferred to,  appear  to  have  been  gradually  uplifted,  and  to  have  attained  their 
present  elevation  at  about  the  commencement  of  the  Pleistocene  era.  In  the 
case  of  the  Alps,  the  final  elevatory  movements  must  have  been  of  terrific 
violence,  and  amounted,  according  to  Sir  R.  I.  Murchison,  "  to  a  total  inver- 
sion, in  many  places,  of  entire  mountains." 

320.  Glacial    Epoch, — During  the  early  part  of  the  Pleistocene  era 
also,  large  portions  of  Europe,  Asia,  and  North  America,  appear  to  have 
gradually  subsided;  and  in  connection  with  these  vast  oscillations  of  the 
crust  of  the  earth,  and,  probably,  as  a  consequence  of  the  changes  occasioned 

QUESTIONS. — What  -were  some  of  the  geographical  features  of  the  globe  at  the  com- 
mencement of  tho  Tertiary  epoch  ?  What  changes  of  land  and  of  climate  took  place  over 
the  northern  hemisphere  at  the  commencement  of  the  Pleistocene  era  ? 


*  Any  one,  says  Sir  R.  J.  Murchison  (Proc.  Royal  Soc.,  1S51,  p.  57),  who  will  climb 
peaks  of  the  Alps  rising  8,000  or  9,000  feet  above  the  level  of  the  sea,  in  the  vicinity  of 
Lake  Lucerne,  may  satisfy  himself,  that  the  crystalline  schists  and  slates  forming  their 
summits  were  once  mere  mud,  deposited  from  water,  at  the  same  time  as  the  slightly 
consolidated  clays  which  underlie  the  city  of  London. 


CAINOZOIC      PERIOD.  295 

by  them  in  the  distribution  of  land  and  water,  the  climate  of  the  temperate 
parts  of  the  northern  hemisphere,  which  was  before  genial,  experienced  a 
great  reduction  of  temperature. 

This  epoch  of  the  earth's  history  is  often  spoken  of  as 
the  "glacial"  epoch  or  period,  from  the  circumstance  that 
glaciers  appear  to  have  then  formed  on  almost  all  the 
mountains  of  the  northern  hemisphere  ;  and  it  is  even  the 
opinion  of  many  geologists  that  almost  the  entire  surface 
of  this  hemisphere,  north  (at  least)  of  the  40th  or  50th 
parallels  of  latitude  was  covered  at  this  epoch  with  ice  of 
great  thickness. 

The  traces  of  the  existence  of  ancient  glaciers,  of  great  extent,  in  the 
northern  part  of  the  United  States,  and  in  Northern  and  Central  Europe, 
are  among  the  most  interesting  of  geological  phenomena.  They  are  the 
same  in  every  respect  as  now  result  from  the  action  of  existing  glaciers,  and 
comprise  rocks  grooved,  striated,  and  polished,  large  masses  of  rocks  dis- 
rupted and  transported,  and  the  peculiar  glacial  accumulations  or  ridges  of 
detritus,  which  are  technically  known  as  Moraines.  (See  §  142.)  In  the 
Alps,  unmistakable  evidence  exists  that  the  extent  of  glacial  action  once 
reached  full  fifty  miles  beyond  the  limits  of  the  existing  glaciers.  Scandi- 
navia, in  Europe,  appears,  moreover,  to  have  been  a  sort  of  center  from 
whence  enormous  glaciers,  like  those  which  now  exist  in  Greenland,  once 
radiated  in  all  directions  over  the  continent.  In  Great  Britain  nearly  all  the 
principal  mountains  of  Wales  and  Scotland,  none  of  which  now  reach  the 
limits  of  perpetual  snow,  have  been  also  the  seat  of  glaciers. 

In  North  America  most  distinct  traces  of  glaciers  have  been  discovered  in 
numerous  localities,  upon  the  Green  Mountain  range  of  Vermont,  Massa- 
chusetts, and  New  Tork,  upon  the  Catskills,  and  upon  the  Laurentian  Moun- 
tains of  Canada.  Upon  the  Green  Mountains  of  Vermont  and  Massachusetts, 
where  the  phenomena  have  been  very  carefully  examined  by  Prof.  Hitch- 
cock, the  glaciers  appear  to  have  filled  up  and  moved  down  the  valleys 
opening  into  the  present  valley  of  the  Connecticut  River,  and  the  valleys 
contiguous  to  its  tributaries ;  and  their  course,  following  the  sinuosities  of 
the  valley?,  is  made  clearly  manifest  by  the  deep  furrows  and  strias  which 
they  have  left  upon  the  sides  of  the  adjacent  mountains.*  In  some  instances 

QUESTIONS. — What  name  is  often  given  to  this  epoch?  Do  we  find  evidence  of  the 
existence  of  former  extensive  glaciers  in  the  temperate  zones  of  the  northern  hemisphere? 
What  is  the  nature  of  this  evidence  ? 


*  According  to  Prof.  Hitchcock,  the  following  are  among  the  localities  in  New  Eng- 
land, where  traces  of  ancient  glaciers  are  especially  noticeable :  In  Massachusetts,  on  the 
Westfield  River,  in  Russel ;  near  Huntington ;  at  Sodom  Mountain,  in  Granville ;  and 
on  the  Deerfield  River  and  ita  branches.  In  Vermont,  at  Windham  and  Grafton,  on 
Saxton's  River ;  on  a  branch  of  West  River,  in  Jamaica  ;  on  the  Otta  Queechee,  in  Ply- 
mouth and  Bridgewater  ;  on  the  White  River  and  its  branches ;  and  at  Hancock,  on  tho 
west  side  of  the  Green  Mountain  range. 


296         FIRST     PRINCIPLES     OF     GEOLOGY. 

also,  the  remains  of  immense  moraines,  crossing  the  valleys  and  indicating 
the  termination  of  the  glaciers,  are  still  visible.  The  length  of  one  of  these 
ancient  glaciers  of  Vermont  has  been  ascertained  by  Prof.  Hitchcock  to  have 
been  at  least  eighteen  miles. 

321.  Drift. — The  subsidence  of  land  in  the  northern 
hemisphere,  already  spoken  of  as  occurring  during  the 
early  part  of  the  Pleistocene,  or  Glacial  epoch,  appears  to 
have  continued  until  a  great  part  of  Northern  America, 
Northern  and  Central  Europe  (including  the  British 
islands),  and  Northern  Asia,  were  submerged  beneath  the 
ocean.  In  Northern  America  the  extent  of  this  subsi- 
dence has  been  estimated  at  from  2,000  to  4,000  or  5,000 
feet,  or  sufficient  to  submerge  nearly  all  the  mountains  of 
Canada,  New  York,  and  New  England.  In  Europe,  the 
amount  of  subsidence  has  been  estimated,  for  different 
localities,  at  from  1,000  to  3,000  feet. 

The  evidence  upon  which  geologists  have  arrived  at  these  conclusions  is 
substantially  as  follows: — 

Spread  out  over  a  great  portion  of  the  northern  hemisphere,  and  resting 
upon  rock  formations  of  every  system,  there  is  found  to  exist  a  vast  accumu- 
lation of  abraded  material,  such  as  clay,  sand,  gravel,  and  detached  frag- 
ments of  rock,  termed  bowlders  ;  the  latter  being  sometimes  scattered  loosely 
over  the  immediate  surface,  and  sometimes  inclosed  in  beds  of  clay  or  gravel, 
without  regard  to  gravity  or  any  other  law  of  arrangement.  These  accumu- 
lations, in  some  places,  exhibit  a  stratified  arrangement,  but,  in  general,  their 
appearance  suggests  at  once  the  idea,  that  they  have  been  transported  and 
confusedly  piled  up  by  some  unusual  and  extraordinary  operation  of  water. 

By  the  early  observers,  the  origin  of  these  deposits  was  referred  to  the 
Noachian  deluge,  and  the  general  name  of  Diluvium  (Lat.,  a  deluge)  was 
applied  to  them;  but  as  the  subject  came  to  be  better  understood,  this 
opinion  was  abandoned,  inasmuch  as  it  was  apparent  that  no  transient 
deluge  could  have  produced  the  effects  exhibited ;  and,  at  the  present  time, 
the  whole  formation  is  believed  to  be  mainly  the  result  of  the  long-continued 
and  joint  action  of  water  and  of  ice,  at  a  time  when  the  lands  in  question 
were  partially  or  wholly  beneath  the  ocean. 

The  name  also  by  which  the  formation  is  now  almost  universally  recog- 
nized is  DRIFT,  although  the  terms  "Diluvium,"  "  Diluvial  Drift,"  "Glacial 
Drift,"  "Bowlder  Formation"  and  "Erratic  Block  Group"  are  frequently  used 
as  synonyms. 

QUESTION. — To  what  extent  did  the  subsidence  of  northern  lands  probably  proceed? 
What  is  mainly  the  evidence  which  has  led  geologists  to  these  conclusions  ?  What  name 
has  been  given  to  the  accumulations  of  abraded  material  spread  over  the  northern  hemi- 
sphere f 


CAINOZOIC     PERIOD. 


297 


Fig.  19  if  represents  drift  (6),  confusedly  blended,  and  resting  upon  highly 
inclined  strata  of  the  Silurian  age  (a),  and  covered  with  deposits  of  the  same 
material  regularly  stratified  (c).  Fig.  198  represents  a  section  of  a  drift  ac- 
cumulation of  coarse  gravel,  sand,  and  bowlders,  which  also  contains  deposits 

of  fine  clay. 

FIG.  198. 


FIG.  197. 


322.  Limits  of  the  Drift ,— In  America  the*Drift  extends  from  the 
polar  regions  as  far  south  as  about  latitude  40°.  "  Its  southern  limit  of  con- 
tinuous deposit  in  the  United  States  is  a  line  drawn  from  Long  Island,  through 
Central  Pennsylvania,  to  the  Ohio,  with  occasional  extensions  southward  in 
the  valleys  of  the  Delaware,  Susquehamia,  and  Mississippi."*  In  Europe  all 
traces  of  it  are  lost  in  the  countries  bordering  on  the  Mediterranean.  In  South 
America  deposits  similar  to  the  northern  Drift  have  been  recognized  in  Terra 
del  Fuego,  and  Patagonia. 

The  vertical  range  of  the  Drift  in  this  country  can  be  inferred  from  the 
fact  "  that  all  the  mountain  peaks  of  Northern  America,  east  of  the  Rocky 
Mountains,  are  covered  by  its  water  and  ice-worn  materials,  with  the  excep- 
tion of  several  hundred  feet  of  the  conical  summit  of  Mount  "Washington,  in 
New  Hampshire,  which  is  covered  with  angular  fragments  of  rocks  that  have 
never  been  disturbed  except  by  frost."  In  many  localities  in  New  England, 
New  York,  and  Canada,  beds  of  clay  containing  marine  shells  occur,  in  some 
instances,  at  an  elevation  of  over  500  feet  above  the  present  sea  level,  and 
are  then  overlaid  by  Drift  deposits  of  sand  and  gravel  of  varying  thick- 
ness. In  England  and  Scotland,  moreover,  marine  shells,  mingled  with  the 
Drift,  have  been  found  at  elevations  as  high  as  2,300  feet  above  the  present 
ocean.  According,  also,  to  Sir  Charles  Lyell,  the  shells  occurring  in  the 
Drift  deposits  of  Canada  and  of  Scotland,  arc  of  an  Arctic  type,  and  indicate 
a  qolder  climate  than  now  prevails  in  those  countries.  In  1849,  during  the 
construction  of  the  Rutland  and  Burlington  railroad,  in  "Western  Vermont, 
an  almost  entire  skeleton  of  a  whale  was  found  embedded  in  blue  clay,  of 
the  Drift  formation,  from  ten  to  fourteen  feet  below  the  surface,  f  A  similar 

QxrESfioxs.— What  are  the  horizontal  limits  of  the  Drift  ?  What  is  its  vertical  range 
in  this  country  ? 

*  The  traveler,  starting  from  Northern  New  England,  and  passing  south  along  any  of 
the  great  lines  of  railway,  can  obtain,  from  the  excavations  on  the  sides  of  the  road, 
many  excellent  views  of  sections  of  Drift  accumulations;  and  can  form  a  good  idea  of 
the  nature  and  arrangement  of  the  Drift  material.  He  will  also  observe,  that  south  of 
the  line  above  indicated,  the  gravel  banks  and  bowlders,  which  are  so  characteristic  of 
New  England,  with  occasional  exceptions,  entirely  disappear. 

t  This  skeleton  is  preserved,  and  may  be  seen  in  the  State  Geological  Collection  of 
Vermont,  at  Burlington. 

13* 


298      FIRST     PRINCIPLES     OF     GEOLOGY. 

skeleton  has  been  also  found  in  a  clay-pit  near  Montreal,  fifteen  feet  below  the 
surface,  associated  with  various  species  of  marine  shells.  At  Gardiner,  and 
Augusta,  Maine,  beds  of  clam  and  muscle  shells,  scarcely  distinguishable 
from  those  now  existing  on  the  adjacent  coast,  occur  beneath  deposits  of  sand 
and  gravel  sixty  feet  in  thickness. 

The  Drift  material  is  diffused  very  unequally.  In  some  localities  it  forms  only 
a  slight  covering  over  the  rock-surface,  or  it  may  be  entirely  wanting,  while 
in  others  it  is  piled  up  in  ridges  and  hills  of  several  hundred  feet  elevation. 

323,  Bowlders  , — The  bowlders,  which  are  everywhere  characteristic  of 
the  Drift  formation,  vary  in  size  from  a  few  pounds  to  masses  of  hundreds 
or  even  thousands  of  tons  weight.  They  are  generally  more  or  less  rounded 
in  form,  as  if  water-worn,  and  are  unlike  the  rocks  in  place  which  under- 
lie them.  In  short,  the  whole  physical  condition  of  these  loose  masses  is 
such  that  the  most  superficial  observer  could  hardly  fail  of  arriving  at  the 
conclusion,  that  they  are  foreign  to  the  localities  where  they  occur,  and  must 
have  been  transported  from  a  distance  by  some  powerful  agency. 

FIG.  199. 


In  some  districts  the  bowlders  are  strewn  so  thickly  that  they  almost  con- 
tinuously cover  many  square  miles  of  surface.  This  is  especially  true  of  many 
parts  of  New  England.  Fig.  18,  page  49,  represents  the  appearance  of  the 

QUESTIONS.— What  other  unmistakable  proofs  of  the  former  submergence  of  this  coun- 
try beneath. the  ocean  have  been  obtained  ?  What  is  said  of  the  diffusion  of  the  Drift 
material?  What  is  said  of  the  occurrence  of  bowlders  in  the  Drift  formation?  What 
of  their  number  ? 


CAINOZOIC      PERIOD. 


299 


country  at  Squam,  on  the  coast  of  Massachusetts,  near  Gloucester.  In  other 
districts,  only  single  bowlders,  separated  by  long  intervals,  or  a  few  "  perched 
blocks"  reposing  on  some  height,  will  be  met  with. 

The  size  of  these  transported  blocks  is  often  enormous.  At  Fall  River, 
Massachusetts,  on  the  south  side  of  the  bay,  at  the  mouth  of  the  Taunton 
River,  a  bowlder  of  conglomerate  rock  was  uncovered  in  a  gravel  ridge, 
which  originally  weighed  5,400  tons,  or  10,800,000  pounds.  The  ledges  of 
this  conglomerate  are  met  with  only  on  the  other  side  of  the  bay.  This  re- 
markable bowlder  has  been  entirely  destroyed  for  building  purposes. 

Fig.  199  represents  a  bowlder  (figured  and  described  by  Dr.  Hitchcock), 
located  upon  a  mountain  in  "Whitingham,  Vermont,  which  is  forty  feet  long, 
thirty-six  feet  wide,  twenty-seven  feet  high,  and  is  estimated  to  weigh  3.400 
tons.  This  bowlder  has,  unquestionably,  been  transported  across  a  valley 
1,000  feet  deep  to  its  present  position. 


FIG.  200, 


Fig.  200  represents  one  of  .the  largest  known  bowlders  in  New  England, 
located  at  Danvers,  Mass.  It  is  the  property  of  the  Essex  County  Society 
of  Natural  History,  and  is  carefully  preserved  from  spoliation,  as  a  geological 
curiosity.  Ou  Hoosic  Mountain,  in  the  town  of  Adams,  Mass.,  is  a  bowlder 

QUESTION.— What  of  the  size  of  somo  bowlders  ? 


300       FIRST     PRINCIPLES     OF     GEOLOGY. 

of  granite,  weighing  500  tons,  which  has  been  transported  from  a  ledge  on 
an  opposite  mountain  across  a  valley  1,300  feet  deep,  and  at  the  same  time 
elevated  about  1,000  feet* 

324.  Rocking  Stones  , — Bowlders  of  many  tons  weight  are  sometimes 
met  with  so  nicely  poised  and  balanced  upon  other  rocks  that  they  may  be 
easily  made  to  oscillate  by  the  hand,  though  an  immense  force  would  be  re- 
quired to  dislodge  them.  Such  examples  are  termed  "  rocking  stones."  Fig. 
201  represents  a  rocking  stone  in  Fall  River,  Mass.,  poised  upon  granite,  and 
weighing  160  tons. 

FIG.  201. 


325.  Dispersion  of  the  Drift,— On  examining  the  sur- 
faces of  bowlders  it  is  common  to  find  them  marked  with 
parallel  scratches  (stria))  and  groovings  ;  and  what  is  still 
more  curious,  the  surfaces  of  the  rocks  upon  which  the 
bowlders,  gravel,  and  other  Drift  accumulations  rest,  are 
also  more  or  less  smoothed  and  marked  with  distinct 
linear  striaa  and  furrows,  as  if  the  Drift  had  been  forcibly 
carried  forward,  and  had  scratched  and  worn  them  during 
its  passage. 

It  has  been  conjectured  that  if  the  rocks  of  the  northern  portion  of  this 
country  could  be  laid  bare,  the  traces  of  this  abrading  action  would  be  dis- 
tinctly visible  over  nearly  half  their  surface.  Rocks,  however,  of  slight  con- 
sistency, or  which  have  been  long  exposed  to  atmospheric  influences,  rarely 
exhibit  it.  These  grooves,  or  stria?,  are  sometimes  a  foot  or  more  in  width, 
and  several  inches  deep,  but  most  generally  they  are  a  fraction  of  an  inch  in 
depth,  and  from  a  quarter  of  an  inch  to  two  or  three  inches  in  width.  Some- 

QTJESTIONB. — What  are  rocking  stones  ?  What  may  be  commonly  observed  upon  the 
surfaces  of  bowlders?  What  curious  fact  has  also  been  noticed  respecting  the  rock  sur- 
faces upon  which  the  Drift  rests  ?  What  is  said  of  extent  and  size  of  the  Drift  markings? 

*  The  action  of  ice  in  transporting  similar  large  blocks  of  stone,  has  been  already  noticed, 
and  may  be  advantageously  reviewed  in  this  connection.  (See  §  142, 143.) 


CAINOZOIC      PERIOD. 


301 


times  the  striae  assume  the  form  of  the  most  delicately  cut  parallel  lines,  so 
fine  that  the  aid  of  a  lens  is  requisite  for  their  examination.  Fig.  202  repre- 
sents examples  of  Drift  striae  on  black  limestone,  from  near  Lake  Champlain, 
Yermont. 

FIG.  202. 


Again,  these  markings  and  groovings  on  the  surfaces  of 
ledges,  or  rocks  in  place,  all  trend  in  one  general,  uniform 
direction,  namely,  from  north  to  south,  varying  from  north- 
east to  southwest,  and  from  northwest  to  southeast. 

"In  general."  says  Prof.  Hitchcock,  "they  do  not  alter  their  course  for 
any  topographical  feature  of  the  country ;  but  cross  valleys  at  every  con- 
ceivable angle,  and  even  if  the  strige  run  in  a  valley  for  some  little  distance, 
when  the  valley  curves  the  stria}  will  leave  it  and  ascend  hills  and  moun- 
tains, even  thousands  of  feet  high." 

In  New  England,  New  York,  and  Canada,  Drift  strias  have  been  observed 
upon  the  summit  of  rocks  of  most  of  the  highest  mountains,  and  from  the 
size  and  extent  of  the  furrows,  it  seems  certain  that  the  agency  which  pro- 
duced them,  was  nearly,  or  quite  as  energetic,  as  at  lower  levels."* 

Another  remarkable  circumstance  connected  with  the 
phenomena  of  the  Drift  striae  is,  that  they  are  never  found 

QTTESTIONS.— Do  the  Drift  striae  run  in  any  uniform  direction  ?  At  what  elevations 
have  they  been  observed  ? 

*  On  the  White  Mountains  of  New  Hampshire  Drift  furrows  exist,  at  an  elevation  of 
5,000  feet  above  the  sea — the  greatest  elevation  at  which  they  have  been  found  in  North 
America.  Above  6,000  feet  the  summit  of  Mt.  Washington  appears  to  have  entirely 
escaped  the  effects  of  the  drift  agency.  On  Jay  Peak,  at  the  Northern  extremity  of  the 
Green  Mountain  range,  4,025  feet,  above  the  ocean,  Drift  striae  exist  abundantly.  On 
Mt.  Holyoke,  in  Massachusetts,  furrows  exist  a  foot  wide  and  two  inches  deep.  Upon 
the  Catskills  the  strise  have  been  observed  at  an  elevation  of  2,850  feet,  running  horizon- 
tally north  and  south,  as  if  a  succession  of  icebergs  had  grated  along  the  slopes  of  the 
mountains  during  their  submergence.  Fine  examples  of  these  striations  may  bo  seen 
while  ascending  the  Catskills  by  the  route  to  the  Mountain  House. 


302 


FIRST    PRINCIPLES    OF     GEOLOGY. 


upon  the  south  sides  of  mountains,  unless  for  a  part  of  the 
way  where  the  slope  is  small.  The  north,  northwestern,  and 
northeastern  sides  of  mountains,  which  have  been  exposed 
to  the  drift  agency,  are  also  universally  worn  and  rounded, 
while  upon  the  south,  or  opposite  sides,  the  projections  are 
more  angular. 

Sometimes  the  end  or  side  of  a  ledge  of  rock  bears  evidence  of  having  been 
subjected  to  crushing  force,  which  has  broken  and  dislocated  the  "strata. 
Fig.  203,  which  is  a  section  of  a  slate  quarry,  at  Guilford,  Vermont,  repre- 
sents an  example  of  this  phenomenon,  which  has  been  referred,  by  Prof. 
Hitchcock,  to  the  action  of  a  glacier  or  huge  iceberg  crowding  along  the 
surface. 

FIG.  203. 


Furthermore,  in  the  northern  hemisphere  the  bowlders 
are  always  of  some  variety  of  rock  which  occurs  in  solid 
ledges  in  a  direction  north  of  their  present  position  ;  and, 
in  most  instances,  by  proceeding  north  in  the  direction  of 
the  Drift  strire  in  the  vicinity,  the  localities  from  which 
the  bowlders  of  a  particular  district  are  derived,  can  bo 
found  at  a  greater  or  less  distance. 

In  such  cases  the  blocks  will  usually  bo  found  to  increase  in  size  and  num- 
ber as  we  approach  the  "parent  ledge." 

QUESTIONS.— What  other  remarkable  circumstances  have  been  observed  in  connection 
with  the  Drift  phenomena  ?  Are  we  able  over  to  determine  the  location  from  whence 
bowlders  have  been  transported  ? 


CAINOZOIC       PERIOD. 


303 


The  distance  to  which  bowlders  of  great  size  can  thus  bo  proved  to  have 
been  transported  is  often  very  great.  "Plymouth  Rock"  is  a  bowlder  of 
sienitic  granite,  ledges  of  which  are  found  in  the  vicinity  of  Boston.  The 
north  shores  of  Long  Island  are  strewn  with  bowlders  of  red  sandstone, 
granite,  and  other  rocks,  arranged  in  groups  which  correspond  with  the 
position  of  the  same  ledges  in  Connecticut,  across  the  Sound  to  the  north. 
Most  of  the  other  islands  on  the  New  England  coast  are  also  covered  with 
bowlders  derived  from  the  continent.  Upon  the  bare  granite  summit  of 
Mt.  Katahdin,  the  highest  mountain  in  Maine,  at  an  elevation  of  3,000  feet 
cr  more  above  the  surrounding  valleys,  pieces  of  limestone  containing  fossil 
shells  are  found,  though  no  ledges  resembling  them  are  known,  except  many 
miles  to  the  northwest,  and  at  a  much  lower  level.  In  Russia  bowlders 
have  been  identified  with  ledges  more  than  800  miles  distant,  in  a  northerly- 
direction. 

FIG.  204. 


Upon  the  prairies  of  the  northwestern  States  granitic  bowlders  of  great 
size  (significantly  called  lost  rocks),  which  have,  undoubtedly,  come  from  the 
region  of  the  great  lakes — a  distance  of  300  to  GOO  miles — are  very  common. 
Fig.  204  represents  the  appearance  of  a  bowlder  of  porphyritic  granite  on  the 
prairies  of  Iowa,  west  of  the  Mississippi  (figured  by  Dr.  D.  D.  Owens,  U.  S. 
Geologist),  the  portion  of  which  above  ground  measures  fifty  feet  in  circum- 
ference and  twelve  feet  high.  This  and  other  isolated  blocks  upon  these 
prairies  appear  to  have  been  dropped  rather  than  rolled  into  their  present 
position,  and,  in  the  opinion  of  Dr.  Owen,  they  have  been  brought  from  ex- 
treme northern  regions  by  iceberg?. 

QUESTION. — What  are  some  of  the  facts  which  have  been  ascertained  respecting  the 
transportation  of  bowlders  ? 


304       FIRST     PRINCIPLES     OF     GEOLOGY. 

326.  Theories  of  the  Drift,— Taking  all  these  phe- 
nomena into  consideration  we  become  impressed  with 
the  idea  that  powerful  currents  have  swept,  from  north 
to  south,  over  all  the  region  occupied  by  the  drift  ma- 
terial— carrying  with  them  clay,  sand,  gravel,  and  rock- 
masses — which  have  furrowed  the  rock-surfa6es  as  they 
passed  along,  abraded  and  rounded  the  northern  slopes  of 
mountains,  and  piled  up  vast  accumulations  and  ridges 
of  detritus. 

It  is  not  easy,  however,  to  refer  such  effects  to  any  ordinary  operations  of 
water.  "We  can  conceive  of  no  current  sufficiently  powerful  to  transport 
bowlders  of  tons'  weight  up  steep  acclivities,  over  mountains,  and  from  one 
valley  to  another.  We  know,  moreover,  of  no  sedimentary  conditions  that 
would  permit  bowlders,  sand,  clay,  and  gravel  to  be  piled  up  in  one  indis- 
criminate mass ;  while  the  extent  of  the  erosion  and  smoothing  of  rock-sur- 
faces that  has  taken  place  clearly  indicates  long-continued  action.  Geologists, 
therefore,  have  almost  universally  agreed,  that  ice  as  well  as  water  was  con- 
cerned in  producing  these  phenomena,  and,  in  the  opinion  of  many,  the  physi- 
cal changes  at  present  occurring  in  Arctic  latitudes,  where  the  land  is  worn 
and  wasted  by  glaciers  and  avalanches,  and  where  icebergs  and  icefloes  trans- 
port and  distribute  the  eroded  material  over  the  bed  of  the  ocean,  afford  a 
sufficient  solution  for  all  the  geological  problems  presented  in  the  Drift  forma- 
tion. (See  §§  142,  143.) 

The  theory  of  the  Drift,  which  has  been  originated  by  Lyell,  Hitchcock, 
and  other  authorities,  and  which  is  now  accepted  by  most  geologists,  is  sub- 
stantially as  follows :  It  is  supposed  that  about  the  close  of  the  Tertiary 
epoch  a  subsidence  of  land  took  place  in  the  northern  hemisphere,  which  was 
accompanied  by  a  great  reduction  of  temperature ;  and  that,  as  a  consequence 
of  this  access  of  cold,  glaciers  formed  upon  most  of  the  northern  mountains, 
and,  as  in  Greenland  at  the  present  day,  extended  to  the  sea.  Large  islands 
and  bergs  of  floating  ice,  laden  with  detritus,  were  also  moved  southerly  from 
the  polar  regions  by  oceanic  currents ;  and  these,  as  they  grounded  on  the 
submerged  lands,  pushed  along  all  loose  materials  of  sand  and  pebbles, 
smoothed  and  rounded  the  northern  sides  of  ledges  and  mountains,  and, 
when  fragments  of  hard  stone  were  frozen  into  their  lower  surfaces,  grooved 
and  polished  the  rocks  with  which  they  came  in  contact.  "When  the  ice- 
bergs and  floes  melted,  their  burdens  of  detritus — including  fragments  of 
rock,  both  large  and  small,  which  had  been  frozen  into  them  as  parts  of 
,  glaciers  or  as  coast-ice — would  fall  to  the  bottom  of  the  ocean,  and,  in  this 
way,  bowlders,  as  well  as  finer  materials,  would  be  scattered  over  extensive 
areas.  As  the  land  also  continued  to  sink,  the  glacier  and  coast-ice  would 

QUESTIONS. — What  general  idea  is  acquired  from  a  consideration  of  the  various  Drift 
phenomena  ?  Is  it  possible  to  refer  all  the  effects  of  the  Drift  to  the  agency  of  water  ? 
"What  theory  in  explanation  of  the  Drift  has  been  advanced  and  generally  accepted  ? 


CAINOZOIO      PERIOD.  305 

*  be  lifted  higher  and  higher  along  the  shores,  and,  finally,  be  urged  by  the 
northerly  currents  over  hills  and  mountains,  carrying  a  great  amount  of 
abraded  material  along  with  them.  Finally,  it  is  supposed,  a  gradual  eleva- 
tion of  the  submerged  lands  took  place,  and  that,  during  their  reemergence, 
the  materials  which  cover  them  were  still  further  modified  (modified  Drift) 
by  exposure  to  the  disturbing  and  stratifying  action  of  waves,  ice,  tides,  and 
currents. 

Other  theories  explanatory  of  the  Drift  phenomena  have  been  proposed  by 
geologists  from  time  to  time,  but  no  one  of  them  is  universally  accepted  as 
fully  adequate  to  explain  all  the  facts  recognized.* 

327.  Duration    of   the    Drift    Period,— How  long    the 
Drift  period  lasted  it  is   impossible   to  determine,  but 
from  the  changes   on  the  surface  of  the   earth,  which 
appear  to  have  been  made  during  its  continuance,  it  seems 
to  have  been  considerably  protracted. 

Thus,  in  the  Yalley  of  the  Connecticut  Eiver,  Prof.  Hitchcock  finds  evi- 
dence that  about  1,000  square  miles  of  surface  have  been  denuded  of  sand- 
stone strata  to  the  depth  of  at  least  1,000  feet;  while  in  other  localities  of 
Yermont  and  Massachusetts,  rock  formations,  of  three,  five,  and  even  ten 
thousand  feet  in  thickness,  have  been  removed  by  erosion.  In  the  north  part 
of  Berkshire  County,  Massachusetts,  according  to  Prof.  Emmons,  a  formation 
of  slates  and  limestone,  equivalent  to  more  than  three-fourths  the  present 
elevation  of  the  peak  "Graylock"  (3,600  feet  above  sea-level),  has  been  worn 
away  and  transported  to  a  distance. 

328.  Ancient    Sea-Beaches    and    River-Terraces, — The 
evidence  of  the   gradual  elevation  of  the  lands  of  the 
northern  hemisphere  above  the  ocean,  at  the  close  of  the 
Drift  period,  is  hardly  less  marked  than  that  which  indi- 
cates their  prior  submergence. 

QUESTIONS. — What  is  said  respecting  the  duration  of  the  Drift  period  ?  Have  we  any 
distinct  evidence  of  the  reelevation  of  land  during  the  Drift  period  ?  ' 


*  A  theory  advanced  by  the  Profs.  Rogers,  and  supported  by  some  eminent  European 
authorities,  supposes  the  Drift  phenomena  to  have  resulted  from  the  movement  of  a 
series  of  stupendous  and  rapidly  moving  "waves  of  translation,"  excited  and  kept  in 
motion  by  the  uplifting  of  the  floor  of  an  Arctic  sea,  and  by  undulations  of  the  earth's 
crust  during  an  era  of  earthquake  commotion.  These  waves  moving  southward  over  a 
considerable  portion  of  the  lands  of  the  northern  hemisphere,  and  driving  before  them, 
with  great  velocity,  vast  masses  of  detritus,  are  considered  to  be  agents  adequate  to  pro- 
duce the  results  exhibited  In  the  phenomena  of  the  Drift  formation.  Dr.  Whewell,  who 
has  instituted  a  mathematical  examination  of  the  mechanical  effect  of  such  convulsions, 
arrives  at  the  conclusion  that  if  a  sea-bottom  450  miles  long,  100  miles  broad,  and  500 
feet  below  the  surface  of  the  water,  were  raised  either  at  once  or  by  paroxysmal  lifts, 
waves  of  translation  would  be  produced  sufficiently  powerful  to  effect  the  dispersion  of 
the  whole  northern  Drift. 


306          FIRST     PRINCIPLES     OF     GEOLOGY. 

Ancient  Sea-Beaches. — Along  the  shores  of  every  sea 
or  ocean  there  exists  a  level  margin,  more  or  less  covered 
with  sand  and  gravel,  which  constitutes  the  existing 
beach,  or  sea  margin  :  but  in  many  countries  there  are 
also  found,  at  various  heights  above  the  present  sea-level, 
and  following  the  bays  or  recesses  of  the  land,  similar 
margins  or  terraces,  which  are  known  as  " ancient"  or 
" raised  beaches"  These  give  evidence  of  either  an  ele- 
vation of  the  land  or  a  depression  of  the  ocean,  and  point 
to  times  when  the  sea  and  land  maintained  successively 
different  levels. 

la  Scotland  fifteen  such  ancient  coast-lines  have  been  enumerated ;  at 
some  of  which  the  sea  remained  sufficiently  long  to  excavate  lines  of  deeply 
hollowed  caverns  in  hard  granitic  rocks.  One  such  ancient  coast-line,  or 
escarpment,  has  been  traced  around  nearly  the  whole  of  Great  Britain  and 
Ireland,  at  a  nearly  uniform  elevation  of  thirty  feet  above  the  present  sea- 
level,  and  presents  marks  of  greater  attrition,  i.  e.,  deeper  wave-hollowed 
caves,  etc.,  than  the  modern  line.  "  It  therefore  seems  certain,"  says  Hugh 
Miller,  "that  however  long  the  sea  may  have  stood  against  the  present 
coast,  it  must  have  stood  for  a  considerably  longer  period  against  this  ancient 
one." 

In  New  England  the  remains  of  ancient  sea-beaches  have  been  pointed' 
out  by  Prof.  Hitchcock  at  elevations  above  the  present  sea-level,  varying 
from  less  than  100  to  between  2,000  and  3,000  feet.  One  such  beach  occurs 
upon  the  east  side  of  Mt.  "Washington,  New  Hampshire,  at  an  elevation  of 
2,020  feet;  another  in  the  vicinity  of  the  Franconia  Notch  of  the  "White 
Mountains,  at  a  height  of  2,665  feet  The  most  distinct  beaches,  however, 
are  usually  less  than  1,200  feet  above  the  sea  level;  and,  according  to  Prof. 
Hitchcock,  they  are  often  in  such  a  state  of  preservation  "that  they  cannot 
be  distinguished  from  recent  beaches,  except  that  they  are  sometimes  much 
mutilated  by  erosion."  Many  of  them  also  wonderfully  correspond  in  height 
over  very  extensive  areas,  thus  indicating  that  they  were  formed  contem- 
poraneously. Fossil  shells  have  been  observed  in  these  beaches  in  this  coun- 
try at  an  elevation  of  over  500  feet  above  the  present  ocean  ;  buffin  Great 
Britain  beaches  containing  species  of  shells  that  now  only  inhabit  high 
northern  latitudes — as  the  shores  of  Iceland  and  Spitsbergen — are  found  at 
much  greater  elevations. 

River  Terraces  , — Indications  of  rivers  having  formerly  run  at  much 
higher  levels  than  at  present,  or  in  places  where  no  river  could  now  exist, 
are  common  in  many  parts  of  this  country.  Thus,  along  the  course  of 

QUESTIONS. — What  is  said  of  the  existence  of  ancient  sea-beaches  ?  Do  such  beaches 
occur  in  this  country? 


CAINOZOIC      PERIOD.  307 

most  of  our  rivers  a  succession  of  terraces  may  be  observed,  one  above  the 
other — each  successive  terrace  being  removed  further  back  from  the  present* 
water  level  than  the  one  below  it.  The  number  of  these  terraces  varies  from 
two  or  three  to  ten,  and  they  appear  sometimes  on  both  sides  of  a  stream, 
and  sometimes  on  only  one  side.  On  the  Connecticut  River  the  terraces  in 
some  places  attain  an  elevation  of  over  200  feet  above  the  present  surface  of 
the  water;  and  on  the  Genesee  River,  N.  Y.,  of  over  300  feet.  Remarkably 
distinct  and  parallel  terraces  or  ridges  of  sand,  gravel,  etc.,  containing  recent 
shells,  may  also  be  traced  along  the  borders  of  some  of  the  great  American 
lakes,  at  a  considerable  distance  back  from  their  present  shores,  and  at  ele- 
vations of  from  100  to  200  feet  above  them. 

These  terraces  give  unmistakable  evidence  of  former 
water  levels,  and  are  believed  to  be  mainly  the  result  of 
the  natural  drainage  of  the  continent,  during  the  period 
of  its  gradual  elevation,  subsequent  to  the  Drift  epoch. 

329.  Examples  of  river  action,  where  no  river  or  stream  now  exists,  are 
also  not  uncommon.     At  Orange,  New  Hampshire,  on  the  summit  level,  be- 
tween the  Connecticut  and  Merrimack  Rivers,  there  are  pot-holes  worn  by  the 
action  of  water  in  solid  granite,  at  an  elevation  of  over  600  feet  above  the 
waters  of  the  Connecticut  River.     Similar  phenomena,  at  even  greater  ele- 
vations (1,600  feet  in  one  instance),  have  been  noticed  in  many  other  locali- 
ties in  New  England.     At  Niagara,  from  the  Falls  for  four  miles  down,  there 
is  spread  over  the  surface,  on  both  sides  of  the  river,  reaching  to  the  edge  of 
the  cliffs,  a  deposit  of  fluviatile  (river-like)  character,  containing  fresh  water 
shells  of  the  same  species  as  those  now  found  in  rivers  above  the  Falls.    It  is 
forty  feet  in  thickness,  and  its  bottom  is  250  feet  above  the  present  channel 
of  the  river.     Now,  these  layers  of  sand  and  gravel  could  have  been  deposited 
only  by  water  running  at  their  level ;  and,  consequently,  this  action  must 
have  been  before  the  deep  gorge,  which  at  present  constitutes  the  channel 
of  the  river,  was  excavated  through  them. 

330.  Antiquity   of  the    Drift — The  Drift  formation  is  regarded  as 
marking  the  last  of  great  geologic  changes  which  have  taken  place  upon  the 
surface  of  our  planet ;  and  some  attempts  have  been  made  by  geologists  to 
calculate  the  absolute  time  that  has  elapsed  since  its  termination.     The  most 
favorable  data  for  this  purpose  have  probably  been  obtained  from  the  study 
of  the  Falls  of  Niagara.     Thus,  various  circumstances  (such  as  the  cutting 
of  the  gorge  through  the  fluviatile  deposits  above  noticed)  clearly  indicate  that 
the  Falls  did  not  commence  until  about  the  close  of  the  Drift  epoch ;   and 
that,  since  their  commencement,  they  have  receded — and  eroded  a  deep  rock 
gorge — from  Queenstown,  on  Lake  Ontario,  to  their  present  location,  a  dis- 

QUESTIONS. — What  are  river  and  lake  terraces?  Where  do  they  exist  in  this  country  ? 
What  do  they  indicate  ?  Are  there  any  examples  of  river  action  at  high  elevations  in 
this  country  ?  Enumerate  some  of  them  ?  What  is  said  of  the  antiquity  of  the  Drift  ? 


308       FIRST     PRINCIPLES     OF     GEOLOGY. 

tance  of  seven  miles.  The  time  required  for  this  recession  and  erosion,  judg- 
ing from  the  most  exact  data  that  can  now  be  obtained  respecting  the 
present  excavating  action  of  the  Falls,  cannot,  in  the  opinion  of  Mr.  Lyell, 
be  estimated  at  less  than  35,000  years ;  and,  accepting  this  calculation  as 
approximately  correct,  then  the  close  of  the  Drift  epoch  cannot  approach 
within  some  25,000  or  30,000  years  of  the  time  commonly  assigned  for  the 
creation  and  first  appearance  of  man  upon  the  earth. 

Fossils  of  the  Pleistocene  Epoch, — Besides  marine  shells 
(which  are  generally  crushed  and  broken),  the  Drift  deposits  in  many  locali- 
ties— especially  in  the  Old  "World — abound  in  the  remains  of  large  terrestrial 
mammalia.  From  the  Drift  of  Great  Britain  alone,  there  have  been  ob- 
tained the  bones  of  two  species  of  elephant,  two  species  of  rhinoceros,  of  the 
hippopotamus,  hyena,  tiger,  bear,  and  of  gigantic  species  of  the  elk,  deer, 
and  ox.  Some  of  these  animals  we  now  know  only  as  inhabitants  of  the 
tropics,  but  during  the  Pleistocene  era  (and  probably  before  the  epoch  of  the 
Drift),  it  seems  certain  that  a  species  of  elephant  (Elephas  primigenius), 
known  as  the  mammoth,*  and  a  species  of  rhinoceros,  roamed  over  the  lands 
from  Siberia  to  Britain,  and  that  they  were  fitted  to  endure  the  rigors  of  a 
severe  climate  by  a  covering  of  long  hair  and  closely  felted  wool.  Wo  know 
this  from  the  wide  distribution  of  their  teeth  and  bones,  and  also  from  the 
circumstance,  that  in  Northern  Siberia,  where  the  soil  is  permanently  frozen, 
entire  carcasses  are  not  unfrequently  found  buried  in  the  Drift,  in  a  high 
state  of  preservation.  The  most  remarkable  instance  of  this  kind,  was  the 
discovery,  in  1799,  of  the  entire  carcass  of  a  mammoth  embedded  in  an  ice- 
cliff  on  the  borders  of  the  Arctic  Sea,  near  the  River  Lena.  When  firsf 
seen  by  a  Tungoos  fisherman  it  was  but  partially  exposed  to  view,  but  in 

1803  the  ice  melted  to  such  an  extent  that  the  enormous  carcass  became  en- 
tirely disengaged,  and  fell  down  from  the  ice  crag  upon  a  sand  bank.     In 

1804  the  discoverer  removed  the  tusks,  which  weighed  360  pounds,  and  sold 
them,  while  the  people  in  the  vicinity  carried  away  large  quantities  of  the 
flesh  of  the  animal  to  feed  their  dogs.     In  1806,  when  the  remains  were 
taken  possession  of  by  an  agent  of  the  Russian  government,  the  head  was 
still  covered  by  the  skin,  the  pupil  of  the  eye  was  distinguishable,  the  brain 
remained  within  the  skull,  and  a  long,  shaggy  mane  hung  from  the  neck. 
It  was  also  ascertained  that  the  skin  of  the  body  had  an  abundant  covering 
of  hair  and  reddish  wool,  indicating  that  the  animal  was  fitted  to  resist  a 

QUESTIONS.— Are  there  any  data  which  allow  us  to  approximately  estimate  the  time 
that  has  elapsed  since  its  termination  ?  What  fossils  have  been  found  in  the  drift  de- 
posits? What  extinct  animals  inhabited  Northern  Europe  and  Asia  during  the  Pleisto- 
cene era  ?  What  evidence  have  we  in  relation  to  this  point  ? 


*  The  mastodon  and  the  mammoth,  which  are  often  confounded  by  those  not  familiar 
with  geological  researches,  were  distinct  animals.  The  former  was  an  animal  allied  to 
the  elephant,  yet  differing  from  it  In  some  respects — especially  in  the  form  of  its  teeth  ; 
the  mammoth,  on  the  contrary,  was  a  true  elephant,  but  of  a  different  species  from  the 
elephant  of  the  present  epoch.  (See  Figs.  195, 196.) 


CAINOZOIC       PERIOD.  309 

cold  climate.  This  skeleton,  with  portions  of  the  skin  and  hair,  was  trans- 
ported to  St.  Petersburg,  and  may  now  be  seen  in  the  museum  of  the  Imperial 
Academy  of  that  city.  Other  similarly  preserved  carcasses  of  mammoths, 
and  of  a  species  of  woolly  rhinoceros,  have  since  been  found  in  Siberia,  and 
in  many  localities  in  that  country  the  bones  and  tusks  of  the  former  animal 
are  so  abundant,  that  the  collection  and  sale  of  fossil  ivory  constitutes  a 
regular  business.* 

Some  idea  of  the  number  of  mammoths  that  formerly  roamed  over  the  land 
of  the  British  Islands  may  also  be  formed  from  the  circumstance,  that  the 
fishermen  engaged  in  dredging  for  oysters  on  one  limited  tract  of  the  English 
coast  (that  of  Norfolk),  brought  ashore,  in  the  course  of  thirteen  years  (from 
1820  to  1833),  no  less  than  2,000  grinders  or  teeth,  besides  great  tusks  and 
numerous  portions  of  skeletons. 

331.  Ossiferous  Caverns, — This  name  has  been  given  to 
caverns — found  in  almost  every  quarter  of  the  globe — 
which  contain  accumulations  of  fossil  bones  embedded  in 
hardened  mud,  or  in  layers  of  stalagmite  which  have  been 
deposited  upon  them  by  water  dripping  from  the  roofs  of 
the  caverns. 

These  bones  have  been  derived,  in  part,  from  animals  that  lived  and  died 
in  the  caverns,  or  from  carcasses  of  animals  that  were  dragged  thither  and 
devoured  by  carnivora,  or  were  possibly  drifted  in  by  waves  and  currents, 
while  the  sea  and  land  stood  at  variable  levels. 

In  Europe  many  remarkable  caverns  of  this  character  have  been  discovered, 
and  their  exploration  is  a  subject  of  high  geological  interest.  From  a  cave 
at  Xirkdalc,  in  Yorkshire,  England,  parts  of  the  skeletons  of  between  200 
and  300  hyenas  have  been  obtained,  besides  bones  of  a  species  of  tiger,  bear, 
ox,  deer,  horse,  mammoth,  rhinoceros,  and  hippopotamus.  In  fact,  the  cave 

QUESTIONS. — "What  are  ossiferous  caverns?  What  is  the  assumed  origin  of  the  bones 
found  in  them  ? 


*  The  cliffs  of  frozen  clay  and  gravel,  that  line  the  Arctic  coast  of  Siberia,  are  described 
by  explorers  as  being  the  repositories  of  vast  quantities  of  bones  of  extinct  animals. 
Capt.  Kellet,  who  commanded  one  of  the  expeditions  in  search  of  Sir  John  Franklin, 
states  that  at  Eschscholtz  Bay — a  locality  a  short  distance  south  of  the  Arctic  circle — 
which  he  visited  in  1850-51,  the  fossil  bones  of  animals  are  so  abundant  that  huge  tusks 
and  horns  not  unfrequently  project  up  through  the  soil,  -while  the  soil  itself,  when  turned 
over,  "  exhaled  a  strong  and  disagreeable  odor,  like  that  of  a  well  filled  cemetery."  Capt. 
Kellet  obtained  from  this  locality  the  remains  of  the  mammoth,  horse,  moose-deer,  rein- 
deer, bison,  musk-ox,  the  big-horned  ram,  and  of  some  cetacea  (whales,  etc.). 

The  theory  in  explanation  of  these  facts,  advocated  by  Sir  John  Richardson  and  other 
geologists,  who  have  given  the  subject  attention,  is,  "  that  Arctic  Siberia  was  onco 
warmer  than  now,  and  actually  produced  a  vegetation  sufficient  to  support  a  vast  crea- 
tion of  herbivorous  animals,  such  as  we  now  find  the  remains  of;  and  that  by  some 
catastrophe — some  vast  deluge  or  wave  of  succession — they  were  suddenly  engulfed  on 
the  shores  of  a  sea  where  they  had  their  pasture-grounds." 


310        FIRST     PRINCIPLES      OF      GEOLOGY. 

seems  to  have  been  a  den  of  hyenas  for  ages  previous  to  the  Drift,  during 
which  epoch  its  entrance  was  choked  up  by  detritus  and  remained  un- 
noticed until  the  year  1821.  Another  similar  cave,  at  Torquay,  England, 
which  seems  tonave  been  successively  the  den  of  hyenas,  bears,  and  smaller 
carnivora,  has  yielded  the  remains  "of  more  wild  beasts  than  would  have 
peopled  all  the  menageries  in  the  world."  From  one  compartment  of  this 
cave  some  thousands  of  teeth  of  the  hyena,  the  bear,  and  the  horse,  have 
been  gathered ;  in  another,  the  floor,  for  several  feet  in  depth,  is  composed 
almost  exclusively  of  gnawed  fragments  of  bone ;  while  bones  projecting 
above  the  stiff  soil  of  the  cave  have  been  actually  worn  smooth  by  contact 
with  the  feet  of  the  hyenas  passing  in  and  out.  Other  remarkable  caverns 
have  been  discovered  in  France,  Germany,  Italy,  Australia,  New  Zealand,  etc., 
and  from  caves  in  the  vicinity  of  Palermo,  Sicily,  especiall}',  the  bones  of 
the  elephants  and  hippopotamus  have  been  obtained  in  such  numbers  that 
ship-loads  of  them  have  been  sent  to  foreign  countries  for  agricultural  pur- 
poses. Fig.  205  represents  a  vertical  section  of  a  famous  bone-cave,  at  Gai- 
lenreuth,  in  Germany,  the  floor  of  which  is  literally  paved  with  fossil  bones 
and  teeth,  embedded  in  layers  of  stalagmite. 


Many  of  these  caves  are  certainly  of  vast  antiquity,  inasmuch  as  their 
lower  floors  often  contain  the  remains  of  Pliocene  animals ;  the  middle  de- 
posits, the  remains  of  true  Pleistocene  species ;  while  the  upper  layers  of 
mud  and  stalagmite,  not  unfrequently  inclose  charred  wood,  rude  stone  im- 
plements, and  bones  of  the  human  race.  Their  epoch,  therefore,  as  respects 
their  organic  remains,  must  be  regarded  as  partly  Tertiary  and  partly  recent. 

332.  In  tropical  and  sub-tropical  countries,  where  the 
influences  which  produced  the  Drift  formation  of  the 

QUESTIONS. — What  are  examples  of  remarkable  bone  civerns  ?  To  whnt  periods  of 
geological  time  are  the  origin  and  bone  accumulations  of  tlicse  caverns  referred? 


CAINOZOIC      PERIOD. 


311 


North  did  not  prevail,  the  deposits  of  the  Pleistocene  era 
form  an  -sninterrupted  series  with  those  of  the  preceding 
Tertiary  ages,  and  are  similarly  characterized  by  the  pres- 
ence of  numerous  and  varied  fossils,  and  especially  by  the 
remains  of  extinct  mammalia. 

In  South  America  the  deposits  of  fine  sediments  spread  over  the  great 
plains  known  as  the  "  Pampas"  (which  appear  to  have  been  submerged  dur- 
ing the  Pleistocene  era)  have  yielded  the  remains  of  many  colossal  extinct 
quadrupeds,  the  majority  of  which  appear  to  have  belonged  to  the  order 
Edentata — an  order  which  is  represented  at  the  present  day  by  the  sloths, 
armadillos,  ant-eaters,  etc.  The  largest  and  most  remarkable  of  these  ex- 
tinct animals  was  the  so-called  Megatherium  (Gr.,  //eyaf,  great ;  and  Orjptov, 
animal),  which  resembled,  in  many  respects,  the  sloth,  but  was  perfectly 

FIG.  206. 


colossal  in  its  proportions — its  body  being  from  eight  to  twelve  feet  long, 
seven  to  eight  feet  high,  and  having  a  breadth  across  the  haunches  of  at 
least  five  feet.  Its  thigh  bone  was  three  times  as  large  as  that  of  the  ele-r 
phant ;  its  tail,  nearest  the  body,  was  six  feet  in  circumference ;  and  its  spinal 
marrow,  judging  from  the  opening  in  the  vertebrce,  must  have  been  a  foot  in 
circumference.  Its  fore-feet  were  a  yard  in  length,  by  twelve  inches  in 
breadth,  and  were  terminated  by  gigantic  claws,  set  obliquely  to  the  ground, 
like  those  of  the  mole — a  position  which  would  render  them  digging  instru- 
ments of  great  power.  Fig.  206  represents  an  entire  skeleton  of  this  animal, 
found  in  1789  near  Buenos  Ayres,  and  now  preserved  in  the  Royal  Museum 

QUESTIONS.— What  is  said  of  the  deposits  of  the  Pleistocene  era  in  countries  not  ex- 
posed to  the  Drift  agency  ?  What  remarkable  fossils  have  been  obtained  from  the 
"  Pampas"  of  South  America  ?  Describe  the  Megatherium. 


312      FIRST     PRINCIPLES     OF     GEOLOGY. 

of  Madrid,  Spain.  Notwithstanding  its  great  size  and  strength,  the  Mega- 
therium i3  shown  by  the  structure  of  its  teeth  to  have  been  an  herbivorous 
animal,  and.  probably,  like  the  present  sloths,  fed  on  the  tender  stems, 
leaves,  and  roots  of  trees.  As  its  weight  and  structure  would  not  allow  it  to 
climb  trees  like  the  sloth,  or  burrow  like  the  mole  (which  it  also  resembles 
in  some  respects),  it  is  supposed  that  the  animal  loosed  and  cut  the  roots  of 
trees  with  its  powerful  claws,  and  then,  supported  on  its  haunches  and  enor- 
mously thick  tail,  pulled  them  down  with  its  fore  limbs,  aided  by  the  great 
weight  of  its  body.0 

FIG.  207. 


The  Megatherium  appears  to  have  flourished  in  great  numbers  on  the  vast 
plains  of  South  America,  and  some  traces  of  it  have  even  been  found  as  far 
north  as  Texas,  Georgia,  and  South  Carolina.  It  was  associated  with  a  num- 
ber of  other  colossal  animals  of  a  similar  character ;  one  of  which,  called  the 
Mylodon,  was  but  little  inferior  in  size.  Fig.  207  represents  a  restored  ap- 
pearance of  the  Mylodon. 

QOTBTIONS.— Have  -we  any  evidence  that  animals  allied  to  the  Megatherium  existed  at 
this  epoch  in  North  America  ? 

*  This  supposition  has  received  a  degree  of  confirmation,  from  the  curious  circumstance 
of  the  finding  of  a  skull  of  one  of  the  great  Megatheroid  animals  (the  Mylodon)  in  South 
America,  which  had  been  fractured  longitudinally  in  two  places,  one  of  which  fractures 
was  entirely,  and  the  other  partially  healed.  As  there  was  probably  no  animal  then 
living  in  the  country  of  the  Megatherium,  which  had  the  ability  or  will  to  make  such  a 
wound,  it  has  been  ascribed  to  the  falling  of  a  tree,  which  the  Mylodon  probably  under- 
mined and  overturned  upon  itself. 


CAINOZOIC      PERIOD.  313 

Towards  the  close  of  the  last  century  ex-President  Jefferson  called  atten- 
tion to  the  occasional  discovery,  in  the  limestone  caverns  of  "Western  Virginia, 
of  huge  bones,  which,  from  the  large  size  of  the  claws  attached,  he  supposed 
must  have  belonged  to  a  carnivorous  animal.  Since  then  other  bones  of 
similar  character  have  been  discovered  in  Kentucky,  Tennessee,  Mississippi, 
Alabama,  and  Brazil,  and  a  scientific  examination  of  them  has  shown  that 
they  are  the  remains  of  an  extinct  sloth-like,  herbivorous  animal,  to  which 
the  name  Megalonyx  (Gr.,  fieyae,  great]  and  ovv^  claw)  has  been  given.  It 
is  supposed  to  have  resembled  the  Megatherium  in  form,  and  to  have  been 
of  about  the  size  of  a  large  ox, — using  its  claws  (some  of  which  were  about 
seven  inches  in  length)  to  loosen  and  pull  down  trees,  in  order  to  feed  upon 
their  leaves.  It  was  contemporaneous  with  the  Mastodon  and  Mammoth  in 
the  Yalley  of  the  Mississippi,  and  possibly  survived  them. 

333.  As  has  been  already  stated,  the  Drift  formation  in  North  America 
does  not  extend  as  far  south  as  the  Southern  or  Gulf  States;  and  this  sec- 
tion of  the  country,  during  the  submergence  of  the  more  northern  portions 
of  the  continent,  appears  to  have  been  the  home  of  a  great  number  of  extinct 
species  of  quadrupeds,  as  the  horse,  bison,  hippopotamus,  elephant,  masto- 
don, megatherium,  megalonyx,  and  others ;  since  we  now  find  the  bones  of 
all  these  animals  in  the  latest  Tertiary  strata  of  Georgia  and  South  Carolina 
mingled  with  shells  of  the  same  species  with  those  at  present  living  in  the 
neighboring  waters. 


POST-TERTIARY,    OR     RECENT    EPOCH. 

334.  The  Post-Tertiary,  or  Recent  system,  embraces  all 
the  superficial  geological  accumulations  and  changes  that 
have  taken  place  since  the  close  of  the  "  Drift"  formation, 
or  since  the  present  distribution  of  land  and  sea  has  been 
established.  It,  therefore,  carries  forward  the  geological 
history  of  the  earth  to  the  present  time,  and  introduces 
us  to  the  existing  order  of  things. 

It  is,  however,  difficult,  perhaps  impossible,  to  draw  any  distinct  line  of 
severance  between  the  deposits  of  the  Pleistocene  and  those  of  the  Post- 
Tertiary  epochs.  Both  formations  insensibly  grade  into  each  other,  and  no 
sudden  and  decided  changes  in  the  forms  and  conditions  of  life  took  place  at 
the  termination  of  one  or  the  commencement  of  the  other,  as  occurred,  appar- 
ently, in  the  transitions  between  the  older  systems.  These  facts  are  strikingly 

QUESTIONS.— What  geological  accumulations  are  included  in  the  Post-Tertiary  or  Recent 
system  ?  What  is  said  of  the  connection  of  the  Post-Tertiary  deposits  with  those  of  the 
preceding  eras? 

14 


314       FIRST     PRINCIPLES     OF     GEOLOGY. 

illustrated  in  the  clay  cliffs,  or  "  bluffs,"  which  border  the  Mississippi  River 
from  Baton  Rouge,  in  Louisiana,  as  far  north  as  Kentucky,  and  rise  to  an 
elevation  of  from  50  to  250  feet.  Here  we  have  a  gradually  varying  succession 
of  strata  which  unite  deposits  of  the  Eocene  age,  containing  bones  of  the 
palseotherium,  at  the  base  of  the  cliffs,  with  those  of  the  Pleistocene^  contain- 
ing bones  of  the  extinct  mastodon,  near  the  summit  ;  while  these  last,  again, 
are  covered  by,  and  blend  into,  modern  fluviatile  deposits,  which  entomb  the 
bones  of  buffaloes,  bears,  raccoons,  opossums,  beavers,  and  other  animals  still 
existing  upon  the  Continent. 

335.  The  accumulations  of  the  Post-Tertiary  epoch, 
although  superficial  and  scattered  indiscriminately  over 
the  surface  without  any  determinate  order  of  superposi- 
tion, assume,  nevertheless,  when  taken  in  the  aggregate,  a 
geological  importance  not  at  all  inferior,  so  far  as  amount 
is  concerned,  to  any  of  the  older  stratified  formations. 

They  consist  mainly  of  clays,  sands,  gravels,  and  marls  —  which,  as  the  pro- 
ducts of  the  ordinary  operations  of  water,  are  often  collectively  termed  Allu- 
vium*— -of  peat-mosses,  infusorial  deposits,  calcareous  and  silicious  tufas, 
coral-reefs,  shell-beds,  and  volcanic  accumulations.  The  "raised  beaches" 
and  "river  terraces,"  described  in  connection  with  Pleistocene  deposits,  are 
also  probably  referable  in  part  to  the  Post-Tertiary  system. 

"With  the  exception  of  volcanic  lavas,  limited  deposits  of  calcareous  and 
silicious  springs,  some  consolidated  sands,  shell-beds,  and  coral-reefs,  the' 
Post-Tertiary  system  does  not  include  any  solid  (or  rock)  strata. 

It  should  be  also  here  remarked,  that  many  of  the  deposits  of  this  system, 
which  we  term  "Recent,"  are  only  so  in  a  geological  sense,  or  as  compared 
with  those  of  the  epochs  already  described,  inasmuch  as  the  time  represented 
by  their  formation  undoubtedly  extends  over  a  period  of  many  thousand 
years.  Thus,  we  include  in  this  system  the  "  delta  formations"  of  existing 
rivers  (see  §  154),  which  are  often  of  great  thickness  —  as,  for  example,  the 
Delta  of  the  Ganges,  which,  in  the  vicinity  of  Calcutta,  has  been  ascertained 
(by  boring)  to  consist  of  successive  layers  of  clay,  marl,  and  vegetable  matter, 
of  at  least  480  feet  in  thickness,  and  all  abounding  with  the  bones  and  shells 


.—  What  is  said  of  the  importance  of  the  accumulations  of  the  Post-Tertiary 
Bystem,  BO  far  as  their  relative  amount  is  concerned?  Of  what  do  they  mainly  consist  ? 
Do  they  include  any  solid  strata?  In  what  sense  do  we  use  the  word  "rece»£,"  as  ap- 
plied to  the  formations  of  this  era? 


*  Some  authorities  (as  Hitchcock)  consider  and  designate  all  aqueous  deposits  formed 
subsequent  to  the  Tertiary  epoch  as  alluvial.  Others  (as  Emmons)  restrict  the  term  to 
the  "washed"  accumulations  of  sand,  gravel,  and  earth,  found  upon  the  banks  and 
mouths  of  rivers.  Lyell  defines  alluvium  to  be  "earth,  sand,  gravel,  and  other  trans- 
ported matter,  which  has  been  washed  away  and  thrown  down  by  rivers,  floods,  or  other 
causes,  upon  land  not  permanently  submerged  beneath  the  waters  of  lakes  and  seas." 


CAINOZOIC      PERIOD.  315 

of  animals  still  living  in  the  vicinity.  Again,  the  amount  of  sediment  brought 
down  by  the  Mississippi  to  the  Gulf  of  Mexico  has  been  shown,  by  Mr.  For- 
shay,  an  eminent  engineer,  and  Dr.  Eiddell,  of  New  Orleans  (from  observa- 
tions extending  through  thirty  years),  to  be  between  three  and  four  thousand 
million  cubic  feet  annually ;  and  yet  at  this  rate  it  must  have  required,  ac- 
ccording  to  Mr.  Lyell,  a  period  of  at  least  60,000  years  for  the  river  to  have 
built  up  the  great  accumulations  of  alluvium  which  make  up  its  Delta.* 

336.  Life  Features  of  the  Post-Tertiary  Epoch,— With 
the  exception  only  of  man,  we  know  of  no  remarkable 
living  generic  animal  forms  that  may  not  have  been  in 
existence  upon  the  surface  of  the  earth  at  the  commence- 
ment of  the  Post-Tertiary  epoch. 

Some  species  of  animals,  however,  which  are  known  to  have  been  abundant 
at  the  commencement  of  this  era,  have  since  become  universally  extinct, 
while  others  have  experienced,  as  it  were,  " local  extinctions"  or,  in  other 
words,  have  entirely  disappeared  or  removed  from  countries  and  areas  that 
were  formerly  inhabited  by  them. 

337.  Epoch  of   the  Mastodon    in  North  America, — The  most 
interesting  of  the  animals,  that  have  recently  (in  a  geological  sense)  become 
extinct,  is,  probably,  the  great  American  Mastodon  (mastodon  giganteus), 
which,  in  connection  with  the  Mammoth,  or  fossil  Elephant  (ekphas  primi- 
genius),  appears  to  have  attained  a  great  numerical  development  upon  this 
continent  at  about  the  close  of  the  Pleistocene,  or  tho  commencement  of  the 
Post-Tertiary  epoch.     Geologists  aro  enabled  to  determine  with  certainty  the 
age  at  which  these  colossal  herbivorous  animals  existed  in  this  country,  from 
the  circumstance  that  their  bones  are  found  in  a  partially  petrified,  or  sub- 
fossil  state,  in  superficial  deposits,  lying  above  the  Drift  formation — as,  for 
example,  in  peat-bogs,  or  the  mud  and  marl  deposits  of  existing  ponds  and 
lakes,  the  origin  of  which,  it  would  seem,  cannot  extend  far  back  of  tho  in- 
troduction of  man  upon  this  continentf 

QUESTIONS.— What  facts  prove  the  great  antiquity  of  some  of  the  Post-Tertiary  de- 
posits ?  What  is  said  of  the  life  features  of  the  Post-Tertiary  epocli  ?  What  interesting 
animals  have  hecome  extinct  in  this  country  within  this  epoch  ? 


*  The  area  of  the  Delta  of  the  Mississippi  is  estimated  at  13,600  square  miles,  and 
borings  have  been  made  in  it  to  the  depth  of  600  feet. 

t  Some  have  thought  that  the  mastodons  and  mammoths  did  not  become  entirely  ex- 
tinct in  this  country  until  after  the  advent  of  man,  and  find  a  support  for  their  opinion 
in  various  traditions  of  the  North  American  Indians,  which  represent  their  ancestors  as 
warring  against  certain  colossal  animals,  which  are  described  as  "  tree-eaters,"  and  as 
never  lying  down,  but  leaning  against  a  tree  when  they  slept.  Sir  Charles  Lyell,  how- 
ever, after  a  review  of  all  the  facts  in  the  case,  has  arrived  at  the  opinion  that  the  period 
of  the  extinction  of  the  mastodon,  although  geologically  modern,  must  have  been  many 
thousand  years  ago. 

The  age  of  the  European  mastodons  was  probably  earlier  than  that  of  the  American, 


316       FIRST     PRINCIPLES     OF     GEOLOGY. 

Judging  from  the  distribution  of  their  bones,  the  mastodons  appear  to 
have  existed  most  numerously  in  the  valleys  of  the  Ohio  and  Mississippi, 
and  from  thence,  to  have  roamed  as  far  to  the  northeast  as  New  York  and 
New  England.  Their  remains,  however,  have  been  but  rarely  found  in  New 
England,  and  it  has  been  conjectured  that  the  Hudson  River  may  have  acted 
as  a  barrier  to  their  migrations.  The  mammoth  (or  fossil  elephant)  appears 
to  have  roamed  over  the  same  territories  contemporaneously  with  the  masto- 
don, but  in  much  smaller  numbers. 

In  the  Western  States  the  bones  of  these  animals  are  found  most  com- 
monly in  the  low  places  around  the  salt  licks — spots  that  are  still  frequented 
by  deer  and  other  wild  animals  that  come  to  "  lick"  up  saline  waters.  At 
one  such  locality,  in  Kentucky,  known  as  the  "Big-Bone  Lick,"  about  twenty 
miles  southwest  of  Cincinnati,  it  is  estimated  that  the  bones  of  100  mastodons 
and  twenty  mammoths  have  been  dug  up,  together  with  the  bones  of  the 
megalonyx,  bufialo,  deer,  and  other  animals. 

The  most  complete  skeletons  of  the  mastodon  have,  however,  been  foun  d 
in  swamps  and  peat-bogs,  in  the  States  of  New  York  and  New  Jersey,  in 
which  the  animals  were  probably  accidentally  mired  and  suffocated.*  The 
finest  and  largest  skeleton  in  existence  was  discovered  by  some  laborers  en- 
gaged in  digging  marl  from  a  swamp  in  Newburg,  N.  Y.,  in  the  summer  of 
1845.  It  occupied  a  standing  position,  with  the  head  raised  and  turned  to 
one  side,  and  the  tusks  thrown  upwards — the  position  natural  to  a  quadru- 
ped when  sinking  in  the  mire.  In  the  place  where  the  stomach  lay,  and 
partially  inclosed  by  the  ribs,  there  were  found  about  seven  bushels  of  vege- 
table matter — i.  e.,  bruised  and  chopped  twigs  and  leaves — which,  without 
doubt,  represented  the  food  last  eaten  by  the  animal.  Some  of  these  twigs, ' 
subjected  to  microscopical  examination,  proved  to  be  those  of  a  coniferous 
tree,  probably  the  white  cedar.  This  skeleton  (represented  in  Fig.  208)  was 
purchased  by  the  late  Dr.  John  C.  Warren,  of  Boston,  and  is  now  preserved 
in  that  city.  Its  dimensions  are  as  follows: — Length,  twenty-five  feet; 
height,  twelve  feet ;  length  of  tusks,  ten  feet.  The  total  weight  of  the  bones 
is  2,000  pounds,  and  so  slightly  changed  are  they,  that  they  still  retain  a 
large  proportion  of  their  animal  matter. 

QUESTIONS. — What  geological  evidence  enables  us  to  accurately  determine  these  facts  ? 
In  what  portions  of  this  country  do  the  mastodons  and  mammoths  appear  to  have  existed 
in  the  greatest  number?  In  what  localities  are  their  bones  usually  found?  Describe 
the  circumstances  of  the  discovery  of  the  great  Newburg  mastodon. 


their  remains,  as  before  stated,  having  been  found  somewhat  abundantly  in  Tertiary 
strata,  as  low  down  as  the  Miocene.  The  remains  of  the  European  and  Siberian  mam- 
moths are  also  found  embedded  in  the  Drift  formation,  while  the  remains  of  the  Ameri- 
can mammoths,  according  to  Prof.  Rogers,  are  invariably  found  above  the  Drift.  It 
may  also  be  here  remarked,  that  it  is  generally  conceded  that  the  American  mastodon 
(mastodon  giganteus)  was  of  a  species  peculiar,  and  restricted  to  this  country. 

*  Elephants  at  the  present  day  in  Africa  become  frequently  entangled  and  suffocated 
in  the  swamps  and  mud-holes  which  they  have  entered  for  the  purpose  of  wallowing. 
At  a  recent  meeting  of  the  Boston  Society  of  Natural  History,  an  instance  of  a  consider, 
able  number  of  elephants  having  been  thus  swamped  and  buried,  was  communicated  by 
one  of  the  American  missionaries  stationed  at  Gaboon,  West  Africa. 


CAINOZOIC      PERIOD. 


317 


In  some  instances  there  have  been  found,  in  connection  with  the  skeletons 
of  the  American  mastodons,  tufts  of  hair,  of  a  dun  brown  color,  varying  in 
length  from  two  to  seven  inches — thus  indicating  that  the  animal,  like  the 
Siberian  mammoth,  might  have  been  fitted  to  endure  a  climate  considerably 
colder  than  that  in  which  the  present  elephants  live, 

FiG.  208. 


338.  Dinornis,  or  Extinct  Birds  of  New  Zealand, — Another 
interesting  example  of  the  extinction  of  a  race  of  animals,  within  a  compara- 
tively recent  period,  has  been  afforded  us  by  recent  discoveries  in  New 
Zealand,  the  history  of  which  furnishes  a  beautiful  illustration  of  the  law  first 
elaborated  by  Cuvier,  that  all  the  parts  of  an  animal's  structure  correspond 
and  are  mutually  dependent  upon  each  other.  (See  §  203.)  Thus,  in  1839, 
Professor  Owen,  the  eminent  English  comparative  anatomist,  received  from 
New  Zealand  a  fragment  of  bone,  six  inches  long,  and  broken  at  both  ex- 
tremities, which  had  been  dug  from  a  deposit  of  river-mud.  Applying  to 
this  fragment  the  principles  of  comparative  anatomy,  he  arrived  at  the  con- 
clusion that  it  once  formed  part  of  the  leg-bone  of  a  gigantic  and  unknown 
bird,  somewhat  resembling  the  ostrich,  but  larger  and  heavier.  This  opinion, 
which  was  at  first  received  somewhat  doubtingly,  was,  in  1843,  confirmed 
by  the  discovery  of  a  large  number  of  similar  bones ;  and  it  is  now  fully 
proved  that  there  existed,  in  New  Zealand,  within  a  comparatively  recent 
period,  great  numbers  of  birds,  whose  tracks  would  have  been  as  large  as, 
or  larger,  than  the  largest  fossil  bird-tracks  found  in  the  Valley  of  the  Con- 
necticut River,  and  whose  height,  in  some  instances,  must  have  been  ten, 
and  possibly  fourteen  or  sixteen  feet.*  From  the  bones  already  collected  "** 

QTTEBTIONS.— What  is  kno\vn  respecting  the  recent  extinction  of  a  race  of  birds  in  New- 
Zealand?  

*  At  the  time  of  the  first  discovery  of  the  large  fossil  foot-prints  of  birds  on  the  sand- 
stones of  the  Valley  of  the  Connecticut  Kiver,  some  geologists  urged,  as  an  argument 
against  their  genuineness,  that  it  would  be  impossible  even  to  imagine  the  existence  of 
a  bird  of  such  stupendous  size  as  -would  be  required  for  the  production  of  the  largest 
impressions. 


318         FIRST     PRINCIPLES     OF     GEOLOGY. 

(and  within  the  last  few  years  entire  skeletons  have  been  found)  Prof.  Owen 
has  determined  the  former  existence  of  eleven  species  of  these  birds,  of  vari- 
ous sizes,  which  he  has  referred  to  one  genus,  under  the  name  of  Dinornis 
(Gr.,  deivo?,  terribk;  and  opvi?,  a  Urd}.  They  appear  to  have  been  destitute 
of  wings,  to  have  had  a  powerful  adze-like  beak,  leg-bones  as  large  as  those 
of  an  ox,  and  toe-bones  nearly  equal  to  those  of  an  elephant.  It  is  also  a 
curious  circumstance  that  the  natives  of  New  Zealand  recognize  these  bones 
as  those  of  a  bird,,  which  they  call  the  Moa;  and  from  the  fact  that  the  bonea 


FIG.  209. 


are  usually  found  slightly  buried  in  the  mud  of  rivers,  or  in  caves,  and  are 
sometimes  associated  with  charred  wood,  and  the  bones  of  man,  it  seems 
almost  certain  that  they  lived  during  the  human  epoch.  Prof.  Owen  infers, 
from  the  form  of  the  skull,  and  some  other  points  of  their  structure,  that  they 
were  sluggish,  stupid  birds,  living  on  roots,  and  without  the  instinct,  or  per- 
haps the  ability,  to  escape,  or  defend  themselves.  Fig.  209  represents  the 
appearance  of  a  skeleton  of  one  of  the  largest  species  of  the  Dinornis. 

QUESTION.— Describe  the  Dinornis. 


CAINOZOIC      PERIOD.  319 

339.  Extinct  Bird  of  Madagascar ,— Since  1850  there  have  been 
received  in  Europe,  from  the  Island  of  Madagascar,  the  bones  of  another 
gigantic  bird,  which  was  quite  as  large,  and  possibly  larger,  than  the  largest 
Dinornis  of  New  Zealand ;  and  what  is  still  more  curious,  there  have  been 
also  found  in  connection  with  these  bones,  in  a  deposit  of  recent  alluvium,  a 
number  of  enormous  eggs,  which  are  believed  to  belong  to  the  same  bird. 
Two  of  these  eggs,  and  the  fragments  of  a  third,  are  now  in  the  museum  of 
the  Jardin  des  Plantes,  at  Paris.  The  dimensions  of  one  of  them  are  as  fol- 
lows:— Largest  circumference,  two  feet  nine  inches;  largest  diameter,  one 
foot,  one  and  three-fourth  inches ;  smallest  diameter,  eight  inches.  The 
thickness  of  the  shell  of  this  egg  is  about  an  eighth  of  an  inch ;  its  capacity, 
about  eighteen  English  pints,  or  six  times  the  gross  volume  of  an  ostrich's 
egg,  or  148  times  that  of  an  ordinary  hen's  egg.* 

FIG.  210. 


340.  Dodo  • — "When  the  Island  of  Mauritius,  in  the  Pacific,  was  dis- 
covered, in  1598,  a  bird  called  the  Dodo,  considerably  larger  than  a  swan, 
and  weighing  about  fifty  pounds,  was  so  abundant  that  it  constituted  an  im- 
portant portion  of  the  food  of  the  inhabitants,  but  within  the  course  of  a  few 
years  it  became  entirely  extinct,  and  its  bones  are  now  found  only  in  the 
recent  alluvial  deposits  of  that  island.  Two  heads,  a  foot,  some  feathers,  and 
a  few  paintings,  have,  however,  been  preserved  in  the  museums  of  Europe, 
and  these  now  constitute  the  only  proofs  of  the  existence  of  a  large  bird, 
which  was  certainly  living  within  the  last  200  years.  Fig.  210  represents 
the  appearance  of  the  Dodo. 

QUESTIONS.— What  is  said  of  the  extinct  birds  of  Madagascar  ?  What  were  the  circum- 
stances of  the  extinction  of  the  Dodo  ? 


*  M.  St.  Hilaire,  an  eminent  French  naturalist,  considers  it  quite  probable  that  this 
bird,  which  he  calls  the  jEpyornis,  may  have  had  an  existence  within  the  historic  period, 
and  have  given  origin  to  the  famous  Eastern  story  of  the  Roc.  (See  "  Arabian  Nights.") 


320        FIRST     PRINCIPLES     OF     GEOLOGY. 

According  to  Prof.  Owen,  we  possess  ample  evidence  also  of  the  existence, 
in  England,  at  the  time  of  the  invasion  of  Julius  Cassar  (2,000  years  ago), 
of  three  distinct  species  of  animals — i.  e.,  two  gigantic  species  of  ox,  and  one 
of  the  reindeer — all  of  which  are  now,  however,  extinct.  In  Ireland  a  large 
species  of  elk  became  extinct,  probably  not  long  after  the  island  was  inhabited 
by  man. 

341.  Examples  of  the  local  extinction  of  animals,  or  their  entire  disappear- 
ance from  areas  formerly  inhabited  by  them,  are  common  and  familiar.  In 
Great  Britain  the  wolf  and  the  beaver  have  become  extinct  within  the  last 
200  years.  The  "  Great  Auk,"  or  Northern  Penguin,  which  was  formerly 
abundant  on  the  coasts  of  Iceland,  Greenland,  and  Norway,  is  not  certainly 
known  to  have  been  seen  since  1844.  In  this  country,  every  one  is  familiar 
with  the  fact,  that  with  the  removal  of  the  forests  many  wild  animals  have 
almost  entirely  abandoned  the  regions  formerly  frequented  by  them,  and 
have  moved  westward.  According  to  Prof.  Owen,  some  animals,  occupying 
circumscribed  provinces,  which  are  being  broken  in  upon  by  new  conditions, 
may  also  be  regarded  as  rapidly  tending  to  extinction — as,  for  example,  tho 
musk-ox,  or  Arctic  buffalo,  the  beaver,  kangaroo,  ostrich,  and  possibly  the 
elephant.  It  is  thus  evident,  that  while  the  inorganic  materials  of  our  planet 
are  being  worn  down,  shifted  and  reconstructed  into  new  arrangements,  its 
vitality  is  also  undergoing  corresponding  modifications,  redistributions,  and 
even  extinctions. 

342.  Epoch  of  Man, — It  is  from  the  superficial  deposits 
of  the  Post-Tertiary,  or  Kecent  epoch — namely,  the  peat- 
mosses, alluvial  sands  and  clays,  cave  deposits,  coral  and 
shell  conglomerates — that  the  geologist  first  obtains  un- 
mistakable evidence  of  the  existence  of  the  human  race 
upon  the  surface  of  our  planet. 

As  regards  the  exact  time,  however,  when  the  creation 
and  first  appearance  of  man  took  place,  geology  gives  us 
no  definite  information  ;  but  this  much  may  be  safely 
stated,  "that  the  scriptural  record,  in  which  man  is  re- 
presented as  the  last  born  of  creation,  is  opposed  by  no 
one  geologic  fact." 

Furthermore,  the  fair  presumption,  reasoning  from  geological  evidence 
alone,  is,  that  man  was  not  called  into  being  until  after  the  commencement 
of  the  present  geological  era,  and  until  after  the  time  when,  in  the  north- 
ern hemisphere,  the  sea  and  land  had  received  their  present  configuration, 
and  were  peopled  by  those  genera  and  species  which  yet  inhabit  their  lands 
and  waters. 

QUESTIONS. — What  other  instances  of  the  total  or  partial  extinction  of  animals,  within 
a  comparatively  recent  period,  can  be  cited  ?  In  what  geological  formations  do  we  first 
find  evidence  of  the  existence  of  man  ?  What  inference  can  be  fairly  drawn  from  geo- 
logical investigations  respecting  the  comparative  antiquity  of  the  human  race? 


CAINOZOIC      PEKIOD. 


321 


Many  interesting  examples  of  the  discovery  of  the  remains  of  man  in  a 
truly  fossilized  state,  or  under  conditions  which  give  them  an  antiquity  an- 
terior to  that  of  any  definite  period  of  history,  are  on  record.  Thus,  on  the 
site  of  the  city  of  Glasgow,  there  have  been  dug  up,  since  1781,  from  a  con- 
siderable depth,  three  rude  canoes  or  boats,  one  of  which  reposed  on  a  bed 
of  sea-sand,  a  quarter  of  a  mile  from  the 
river  Clyde,  and  twenty -six  feet  above  its 
present  high- water  level.  Mr.  Robert  Cham- 
bers, of  Scotland,  who  investigated  the  cir- 
cumstances of  these  discoveries  (the  last 
being  in  1854),  states  "  that  we  have  scarcely 
an  alternative  to  the  supposition,  that  when 
these  vessels  foundered,  and  were  deposited 
where  in  modern  times  they  have  been  found, 
the  Firth  of  Clyde  was  a  sea,  several  miles 
wide  at  G-iasgow,  and  covering  the  site  of  a 
portion  of  the  city."* 

"Within  the  present  century  there  have 
been  obtained,  from  the  coast  of  Guadaloupe, 
one  of  the  "West  India  islands,  embedded 
in  hard,  compact  limestone,  a  number  of 
fragmentary  human  skeletons,  one  of  which 
(see  Fig.  211)  now  constitutes  a  conspicu- 
ous feature  of  the  geological  collection  of 
the  British  Museum,  while  portions  of 
others  are  preserved  in  the  Museum  of 
the  Jardin  des  Plantes,  at  Paris,  and  in  the 
Museum  of  the  Medical  College  of  Charles- 
ton, S.  C.  "When  these  fossil  skeletons 
were  first  discovered,  they  were  regarded  by 
some,  as  constituting  of  themselves,  ample 
evidence  of  the  existence  of  the  human  race  during  a  remote  geological 
epoch ;  but  a  careful  examination  of  the  rock  inclosing  the  bones,  has  since 
shown,  that  it  is  of  very  recent  origin — of  a  variety,  in  fact,  that  is  even  now 
continually  in  the  process  of  formation  (see  §  66) — being  composed  of  minute 
fragments  of  shells  and  corals,  of  species  now  inhabiting  the  adjacent  seas, 
ground  down  by  the  waves  and  consolidated  along  the  sea  margin.  The  fact 
that  the  same  rock  has  been  also  found  to  inclose  fragments  of  pottery,  stone 
arrow-heads,  and  pieces  of  carved  wood  in  a  high  state  of  preservation,  fur- 
ther identifies  the  age  of  these  bones  as  historically  recent,  and  renders  it  cer- 
tain that  they  are  the  remains  of  the  ancient  Indian  inhabitants  of  the  island. 

QUESTION.— Are  the  remains  «f  man  ever  found  in  a  fossil  state  ? 


*  One  of  these  canoes— still  preserved  in  a  museum  at  Edinburgh— contained,  when 
discovered,  a  beautifully  shaped  and  polished  stone  hatchet ;  which  circumstance  would 
seem  to  indicate  that  the  use  of  iron  was  unknown  to  the  builders  of  the  vessel. 


322        FIRST     PRINCIPLES     OF     GEOLOGY. 

In  Europe  the  works  and  bones  of  man  have  been  often  found  in  caverns, 
embedded  in  mud  or  layers  of  stalagmite,  and  in  such  close  proximity  to  the 
remains  of  fossil  animals  that  some  have  supposed  that  representatives  of 
the  human  race  must  have  lived  contemporaneously  with  the  extinofr  species 
of  the  Tertiary  epoch.  A  careful  investigation  of  all  the  phenomena  has, 
however,  in  almost  every  case,  entirely  dissipated  any  such  conclusions,  or  at 
least  rendered  them  extremely  doubtful. 

343.  Economic  Products  of  the  Tertiary  and  Post- 
Tertiary  Systems, — In  an  economic  point  of  view,  the 
materials  of  the  Tertiary  and  Post-Tertiary  systems  are 
of  vast  and  universal  value. 

They  include,  for  example,  most  of  the  clays  used  for  pottery,  bricks, 
and  other  fictile  purposes;  the  supplies  of  silicious  sand  used  for  glass- 
making,  the  preparation  of  mortar  and  the  molds  of  metal-smelters ;  and  the 
gravels  used  for  road  making.  In  this  country  nearly  all  the  fine  clays  suit- 
able for  pottery  and  modeling,  are  obtained  from  Eocene  and  Miocene  Terti- 
ary deposits  along  the  Atlantic  coast — especially  from  Martha's  Vineyard, 
Long  Island,  and  New  Jersey — while  the  coarser  clays  of  the  northern  and 
interior  portions  of  the  country,  which  are  extensively  used  for  brick-making, 
are,  for  the  most  part,  referable  to  the  Drift  formation.  Great  accumula- 
tions of  coarse  sand  and  gravel  are  also  almost  everywhere  characteristic 
materials  of  the  Drift  formation. 

In  California.  Australia,  and  the  Ural  Mountains,  drift,  or  fluviatlle  sands 
and  gravels,  are  the  main  repositories  of  gold;  and  in  Brazil  and  India,' 
of  gems  and  precious  stones.  Peat  and  marl  are  other  familiar  economic 
products  of  the  latest  geological  formations. 


CONCLUSION. 

344.  IN  the  sketch  of  the  geological  divisions  of  the  earth's  crust,  embraced 
tn  the  foregoing  chapters,  not  a  thousandth  part  of  what  might  have  been  told 
respecting  the  ancient  history  of  our  earth  and  its  inhabitants  has  been  given. 
Sufficient,  however,  it  is  believed  has  been  stated,  to  enable  the  student  to 
obtain  a  general  and  comprehensive  idea  of  the  most  important  facts  and 
theories  which  have  resulted  from  geological  studies  and  explorations,  and 
which  are  now  recognized  as  constituting  the  fundamental  elements  of  geo- 
logical science. 

Turning  back  the  record  of  the  earth,  as  revealed  to  us  in  the  successive 
groups  of  strata  which  compose  its  crust,  one  cannot  fail  to  be  impressed 
with  the  idea  that  there  has  been  a  continual  progress  in  the  condition  of 

QUESTIONS.— What  is  said  of  the  economic  products  of  the  Tertiary  and  Post-Tertiary 
systems  ?  Enumerate  some  of  these  products. 


CONCLUSION.  323 

our  planet,  whereby  its  surface  has  become  gradually  fitted  for  the  existence 
and  development  of  higher  forms  of  animal  and  vegetable  life,  and  that  these 
have  appeared  at  successive  epochs,  as  if  by  special  acts  of  creation.  Thus, 
at  one  stage  of  the  earth's  history — the  era  of  the  Metamorphic  rocks — plants 
and  animals  do  not  appear  to  have  existed.  It  is  true,  that  the  evidence  on 
this  point  is  merely  negative,  and  the  geologist  cannot  say  with  certainty  that 
life  was  not  coeval  with  the  globe  itself;  but  the  fair  presumption,  from  a 
great  number  of  facts  is,  that  the  earth,  anterior  to  the  epoch  of  the  deposi- 
tion of  the  Huronian  or  Cambrian  rocks,  was  not  in  a  condition  to  support 
life  under  any  of  its  forms. 

As  we  ascend  higher,  however,  in  the  series  of  strata,  we  find  vestiges  of 
organic  beings — first,  in  the  rocks  at  the  base  of  the  Silurian  system.  Among 
plants,  we  have  first  sea-weeds,  and  afterwards,  in  the  Devonian  and  Car- 
boniferous systems,  land  plants ; — ferns,  club-mosses,  and  gigantic  endogens 
predominating  in  the  coal-measures;  palms,  cycadacese,  and  pines  in  tho 
Oolite  ;  and  exogenous  or  true  timber  trees  in  the  Tertiary  and  current  eras. 

In  the  animal  kingdom,  we  find  evidence  that  zoophytes,  radiata,  mollusca^ 
and  articulata  existed  for  ages  in  the  broad  seas  of  the  Lower  Silurian  epoch, 
before  there  were  any  higher  forms; — all,  however,  being  perfect  of  their 
kind,  and  as  admirably  constructed  as  any  representatives  of  the  same  orders 
now  peopling  existing  seas. 

Next  to  these  invertebrata  appear,  in  the  deposits  left  by  the  waters  of 
the  Upper  Silurian  and  Devonian  epochs,  the  first  vertebrate  animals,  in  the 
form  of  fishes.  After  these  come  land  animals,  of  which  the  first  were  rep- 
tiles, universally  allowed  to  be  the  type  of  animal  life  next  in  advance  from 
fishes,  and  to  be  connected  with  the  latter  by  the  links  of  an  insensible  gra- 
dation. From  reptiles  we  advance  to  birds  and  mammals,  which  last  appear 
to  be  represented  in  the  commencement  by  the  lowest  forms  of  their  class, 
viz.,  the  Marsupalia.  In  the  Lias  and  Oolite,  reptiles  attain  their  greatest 
development,  and  are  the  predominant  forms.  In  the  Tertiary  epoch,  how- 
ever, huge  mammalia  prevail,  and  these,  in  time,  give  place  to  other  and 
existing  species,  with  Man,  the  highest  representative  of  their  class,  and  tho 
crowning  form  of  created  existences. 

According,  moreover,  to  the  testimony  of  the  most  eminent  geologists  and 
anatomists,  the  human  form  is  that,  toward  which,  as  to  their  archetype,  all 
other  organic  creatures  have  been  tending.  Oken,  tho  eminent  German 
anatomist,  says,  "  Man  is  the  sum  total  of  all  the  animals."  Prof.  Owen  of 
England,  "supreme  in  his  own  especial  walk  as  a  comparative  anatomist," 
asserts  that  "  the  recognition  of  an  ideal  exemplar  for  the  vertebrated  ani- 
mals, proves  that  the  knowledge  of  such  a  being  as  man  must  have  existed 
before  man  appeared.  For  the  Divine  mind  that  planned  the  archetype  also 
foreknew  all  its  modifications.  The  archetypal  idea  was  manifested  in  the 
flesh,  under  divers  modifications,  upon  this  planet,  long  prior  to  the  exist- 
ence of  those  animal  species  that  actually  exemplify  it." 

The  same  idea  is  also  recognized  by  Prof.  Agassiz,  who  expresses  him- 
self as  follows : — "  It  is  evident  that  there  is  a  manifest  progress  in  the  suc- 
cession of  beings  on  the  surface  of  the  earth.  This  progress  consists  in  an 


324      FIRST     PRINCIPLES     OF     GEOLOGY. 

increasing  similiarifcy  to  the  living  races,  and,  among  the  vertebrates,  especi- 
ally, in  their  increasing  similarity  to  man.  But  this  connection  is  not  the 
consequence  of  a  direct  lineage  between  the  races  of  different  ages.  There 
is  nothing  like  parental  descent  connecting  them.  The  fishes  of  the  Palaeo- 
zoic age  are  in  no  respect  the  ancestors  of  the  reptiles  of  the  secondary  age, 
nor  does  man  descend  from  the  mammals  which  preceded  him  in  the  Terti- 
ary age.  The  link  by  which  they  are  connected  is  of  a  higher  and  imma- 
terial nature ;  and  their  connection  is  to  be  sought  in  the  view  of  the  Creator 
himself,  whose  aim  in  forming  the  earth,  in  allowing  it  to  undergo  the  suc- 
cessive changes  which  geology  has  pointed  out,  and  in  creating  successively 
all  the  different  types  of  animals  which  have  passed  away,  was  to  introduce 
man  upon  the  surface  of  the  globe.  Man  is  the  end  toward  which  all  the  animal 
creation  has  tended  from  the  first  appearance  of  Hie  first  Palaeozoic  fishes." 

345.  The  study  of  the  systems  and  periods  of  the  geologist  also  leads  to  the 
conclusion,  that  in  ah1  times  past  the  agencies  which  have  operated  to  change 
and  modify  the  rock  materials  of  the  globe  have  been  the  same ;  that  then  as 
now,  sands  and  sandstones,  gravels  and  conglomerates,  shales  and  clays,  vege- 
table and  animal  debris,  were  accumulated  and  consolidated  in  precisely  the 
same  way  and  by  similar  agencies.     Some  geologists  (who  have  been  termed 
Catastrophists)  incline,  however,  to  the  opinion  that  geological  agencies,  in 
order  to  have  produced  the  results  recognized,  must  have  acted  in  the  .earlier 
epochs  of  the  world  with  greater  intensity,  and  also  simultaneously  over 
wider  areas,  than  at  the  present  day ;  while  another  class  (who  have  been 
termed  Quietists)  consider  the  movements  now  going  on  upon  the  surface  of 
the  earth,  and  coming  under  the  observation  of  men,  as  sufficient,  if  extended 
through  indefinite  periods  of  time,  to  account  for  all  the  phenomena  presented 
in  the  crust  of  the  earth,  without  the  necessity  of  attributing  to  the  forces 
any  greater  intensity  of  action  than  they  now  exhibit.     This  latter  belief 
(which  is  especially  advocated  by  Sir  Charles  Lyell  in  his  great  work,  "  Prin- 
ciples of  Geology")  is  certainly  in  accordance  with  the  spirit  of  right  phi- 
losophy, though  many  problems  in  geology  seem  to  find  a  solution  only 
through  the  admission  of  the  former  hypothesis. 

346.  Geology  and  the   Bible. — It  is  sometimes  urged  against  the 
study  of  geology,  that  its  teachings  are  inconsistent  with,  or  opposed  to, 
those  of  inspiration.     To  enter  into  any  discussion  of  this  subject,  with  a 
view  of  proving  to  the  contrary,  would  be  foreign  to  the  object  of  the  present 
work ;  but  it  may  not  be  inappropriate  to  call  the  attention  of  those,  who 
have  neither  the  time  nor  opportunity  for  examining  the  points  at  issue  suffi- 
ciently to  arrive  at  an  independent  opinion,  to  the  circumstance,  that  many 
of  the  leading  authorities,  at  the  present  day,  in  geology — Dean  Buckland, 
Hugh  Miller,  Whewell,  Sedgwick,   Hitchcock,  Emmons,  and    many  others, 
are  men  whose  Christian  faith  and  character  has  never  been  questioned ;  and 
if  these  persons  can  find  no  serious  inconsistency  between  the  teachings  of 
science  and  religion,  the  presumption  is  a  fair  one  that  none  in  reality  exists. 
"  No  truths  established  by  studying  the  works  of  God  can  interfere  with 
truths  revealed  by  His  Word." 


APPENDIX. 


ALTHOUGH  geology  may  be  taught  exclusively  from  a  text-book,  yet  in  no 
way  can  a  knowledge  of  the  science  be  gained  so  readily  and  so  pleasantly 
as  by  combining  with  the  lesson  of  the  book  an  examination  of  actual  speci- 
mens, the  inspection  of  geological  plates  and  illustrations,  and  by  excursions 
to  natural  sections  and  to  examples  of  rock  formations. 

It  is  an  error  to  suppose  that  an  expensive  cabinet  of  geological  and 
mineralogical  specimens  is  necessary  to  illustrate  efficiently  a  course  of  geo- 
logical study.  On  the  contrary,  every  teacher  and  student  can  readily,  and 
with  little  or  no  expense,  collect  specimens  of  almost  every  important  variety 
of  rock  and  of  many  of  the  fossils  which  characterize  the  great  geological 
groups  and  systems.  Every  section  of  country  affords  an  abundance  of  some 
classes  of  specimens.  Thus,  the  coast  of  New  England  abounds  in  granites, 
syenites,  quartz-rocks,  trap-rocks,  and  porphyries ;  and  the  country  adjacent 
to  the  Green  and  Appalachian  range  of  mountains,  in  metamorphic  rocks, 
namely,  clay-slates,  talcose,  mica,  and  hornblende  schists,  and  many  varieties 
of  quartz,  and  crystalline  limestones  or  marbles.  In  the  Yalley  of  the  Con- 
necticut, in  New  Jersey,  Eastern  Virginia,  and  North  Carolina,  we  have 
shales  and  sandstones  of  Mesozoic  age  ;  among  the  Catskills  of  New  York, 
sandstones  and  fossils  of  Devonian  age;«  along  the  Atlantic  coast,  from 
Martha's  Vineyard  to  Texas,  Tertiary  strata  and  fossils ;  in  "Western  New 
York  and  throughout  the  "Western  States,  Silurian  rocks  and  fossils;  while 
Pennsylvania,  Virginia,  North  Carolina>  and  almost  every  State  West,  afford 
magnificent  examples  of  the  coal  formation,  with  its  characteristic  fossils. 
In  all  these  sections  of  country,  moreover,  there  are  always  numbers  of  per- 
sons who  will  gladly  and  freely  exchange  suits  of  specimens  from  their  own 
localities  for  those  of  other  and  remote  districts. 

As  a  guide  for  collecting,  it  is  suggested  to  teachers  and  students  that  they 
should  first  endeavor  to  obtain,  and  render  themselves  thoroughly  familiar 
with,  the  following  specimens: — 

EOCK  SPECIMENS. —  Granite;  Syenite;  Gneiss;  Clay- Slate;  Clay- Shale; 
Mica- Schist;  Talcose- Schist;  Hornblende- Schist;  Quartz-Rock;  Porphyry; 
Greenstone ;  Basalt ;  Lava ;  Serpentine ;  Limestone,  crystallized,  earthy,  and 
magnesian ;  Sandstones,  red,  white,  and  brown ;  Marl ;  Calcareous  Tufa,  Stal- 
actite or  Stalagmite ;  Conglomerate ;  Coal,  anthracite  and  bituminous ;  Lignite. 

MINERALS,  which  are  the  essential  components  of  important  rocks,  or 
are  frequently  embedded  in  them  -.—Quartz,  crystallized  and  massive;  Agate; 


326  APPENDIX. 

Chalcedony;  Jasper;  Garnet;  Hornblende;  Feldspar;  Mica;  Augite;  Talc; 
Steatite;  Tourmaline;  Calcareous  Spar ;  Sulphate  of  Lime,  or  Gypsum; 
Sulphur ;  Plumbago ;  Bitumen ;  Bituminous  Shale ;.  Baryta. 

ORES  OF  THE  METALS. — Iron  Pyrites  (sulphide,  or  sulphuret  of  iron]  • 
Magnetic  Oxyd  of  Iron  ;  Red  and  Brown  Hematite ;  Bog-Iron  Ore ;  Ores  of 
Manganese  ;  Galena,  or  Sulphuret  of  Lead ;  Native  Copper ;  Carbonates  and 
Sulphurets  of  Copper ;  Red  Oxyd  of  Zinc;  Blende,  or  Sulphuret  of  Zinc. 
Ores  of  other  and  rarer  metals,  as  of  Tin,  Gold,  Silver,  Platina,  Cobalt, 
Nickel,  Antimony,  etc.,  can  be  added  if  convenient. 

Those  who  would  prefer  to  purchase  rather  than  collect  their  specimens, 
can  obtain  elementary  geological  and  mineralogical  collections  of  dealers 
in  New  York  City,  at  moderate  prices.*  At  the  same  time,  the  personal 
collection  of  specimens  is  to  be  recommended  whenever  practicable,  as  the 
information  obtained  in  so  doing  is  of  the  most  lasting  and  practical  character. 

Collections  of  characteristic  fossils  of  the  different  geological  systems  are 
much  more  difficult  to  obtain  than  collections  of  characteristic  minerals  and 
rock  specimens.  Deficiencies  in  this  respect  may,  however,  be  supplied  in  a 
great  degree  by  reference  to  the  plates  and  figures  given  in  most  of  the  ex- 
tended works  and  reports  on  .Geology  and  Palaeontology.  Thus,  the  Reports 
of  the  Geological  Survey  of  the  State  of  New  York  figure,  with  great  minute- 
ness, the  fossils  of  the  Silurian  and  Devonian  rocks  found  in  that  State  ;  the 
Eeport  of  the  Survey  of  Pennsylvania,  the  fossils  of  the  Carboniferous  sys- 
tem ;  and  that  of  North  Carolina,  the  fossils  of  formations  of  the  Mesozoic 
period.  No  difficulty,  however,  will  be  experienced  in  obtaining  specimens 
illustrative  of  all  the  conditions  in  which  fossils  occur ;  as  true  petrifactions, 
incrustations,  casts,  impressions,  etc. ;  and  also  of  specimens  of  rock-masses 
Which  have  been  formed  by  the  aggregation  of  particles  or  fragments  of 
organic  structures,  as  of  shells,  corals,  encrinites,  etc. 

"Whatever  may  be  the  text-book  used,  the  teacher  will  find  ifc  very  advan- 
tageous to  have  other  books  on  the  subject  of  geology  at  command,  from 
which  he  may,  from  time  to  time,  illustrate  any  particular  subject  under  con- 
sideration, by  reading  or  quoting  examples  or  descriptions  of  phenomena,  or 
by  exhibiting  plates  and  diagrams  additional  to  those  included  in  the  lesson. 
In  this  way,  the  recitation  may  be  made  to  partake  of  the  character  of  a 
familiar  lecture,  and  the  interest  of  the  student  is  encouraged  and  sustained ; 
and  unless,  in  the  study  of  the  natural  sciences,  the  interest  is  awakened,  all 
routine  instruction  will  profit  but  very  little.  Among  the  books  especially 
worthy  the  attention  of  teachers  and  students,  the  following  may  be  recom- 
mended : — First,  the  Report  of  the  Geological  Survey  of  one's  own  State. 
In  most  of  the  States  such  reports  have  been  published,  and  can  often  be 
procured  gratuitously.  They  furnish  local  examples  of  geological  phenomena, 
information  respecting  the  age  and  character  of  the  rocks  in  one's  immediate 
vicinity,  and  the  localities  where  specimens  of  particular  rocks,  minerals,  and 
fossils  are  obtainable.  Within  the  last  few  years  many  reports  of  Geological 

*  Further  information  on  this  subject  can  be  obtained  of  the  Publishers  of  this  work, 
Messrs.  IVISON,  PUINNEY  &  Co.,  48  &  50  Walker-street,  New  York. 


APPENDIX.  327 

Surveys  of  tho  U.  S.  Territories  have  been  also  issued  and  distributed  gratui- 
tously by  the  National  Government.  Many  of  these  are  readily  accessible 
in  every  section  of  the  country,  and  contain  much  valuable  information,  with 
numerous  Maps,  Sections,  and  Illustrations. 

From  the  following  list  of  leading,  and  for  the  most  part  inexpensive  geo- 
logical treatises,  selections  can  be  made  according  to  one's  inclination  and 
ability: — Lyell's  " Ekments  of  Geology ;"  Lyell's  "Principles  of  Geology"  (this 
work  is  a  storehouse  of  facts  relative  to  current  geological  events)  ;  De  La 
Beche's  "  Geological  Observer ;"  Mantell's  "  Wonders  of  Geology;"  Mantell's 
"  Medals  of  Creation"  (an  elementary  English  work  on  Palaeontology) ;  Hugh 
Miller's  "  Testimony  of  the  Rocks,"  "  Popular  Geology,"  "  Old  Red  Sandstone," 
"  Footprints  of  the  Creator ;"  Hitchcock's  "  Outlines  of  the  Geology  of  the 
Globe ;"  Hitchcock's  "  Illustrations  of  Surface  Geology ;"  Emmons's,  Hitch- 
cock's, Jukes,  and  Ansted's  Elementary  Treatises  on  Geology  (the  last  two, 
English  publications) ;  Page's  "  Hand-Book  of  Geological  Terms"  (English) ; 
Taylor's  "History  and  Statistics  of  Coal;"  Buckland's  "  Bridgewater  Treat- 
ises;" Dana's  "Elementary  Mineralogy,"  etc.  A  popular  account  of  all  the 
new  facts  and  theories  in  geology,  reported  for  each  successive  year,  will 
also  be  found  in  the  volumes  of  the  Annual  of  Scientific  Discovery. 

Geological  excursions  to  localities  of  interest  afford  an  opportunity  for  ob- 
taining much  practical  information,  conjointly  with  healthful  outdoor  exer- 
cise and  recreation.  It  is  not  necessary  either  to  travel  miles  or  days  to  find 
such  localities.  Sea-cliffs,  river-channels,  the  sides  of  ravines,  mountain 
precipices,  road  and  railway  cuttings,  stone-fences,  clay-beds,  sand  and  gravel 
banks,  quarries,  and  mines,  all  these  are  geological  localities  of  interest ;  and 
although  one  may  have  seen  them  every  day  for  years,  yet  when  examined 
for  the  first  time,  from  a  geological  point  of  view,  they  will  be  found  ex- 
pressive of  many  varied  and  interesting  truths. 

"  In  a  new  and  progressive  science  like  geology,  which  has  still  such  a  wide 
field  of  exploration  before  it,  and  which  calls  in  the  aid  of  so  many  of  the 
other  sciences,  there  is  ample  scope  for  the  energy  and  industry  of  the  most 
talented  and  enthusiastic.  One  individual  may  devote  himself  to  the  mineral- 
ogy of  geology;  another  to  its  physical  problems;  a  third  to  fossil  plants;  a 
fourth  to  fossil  animals ;  a  fifth  to  the  economic  relations  of  tho  science ;  and 
a  sixth  endeavor  to  find  expression  for  the  general  laws  which  it  indicates; 
while  all  may  go  on  as  one  great  brotherhood  in  the  elucidation  of  the  his- 
tory of  the  marvellous  world  we  inhabit.  And  whether  in  collecting  data 
among  the  hills  and  ravines,  by  the  sea-cliff  or  in  tho  mine,  or  in  arranging 
and  drawing  from  these  data  the  warranted  conclusion,  the  earnest  student 
will  find  geology  at  once  one  of  the  most  healthful  and  exhilarating,  as  it  is, 
intellectually,  one  of  the  most  expanding  of  human  pursuits.  And  even 
when  no  professional  object  is  aimed  at,  the  man  of  business,  the  health- 
seeker,  and  the  holyday  tourist,  will  find  it  an  endless  source  of  recreation — 
one  that  need  never  interfere  with  the  comfort  of  a  neighbor,  or  bring  to  the 
observer  one  pang  of  mortification  or  regret." 


. 


INDEX. 


ACALEPHS,  190. 

Acephala,  188. 

Acrogens,  185. 

Adirondac  Mountains,  geology  of,  207. 

Agates,  what  are,  19. 

Agencies,  Aqueous,  133. 

Igneous,  99. 

Air,  action  of,  on  rocks,  134. 
Alabaster,  what  is,  59. 
Algse,  what  are,  185. 
Alluvium,  what  is,  48. 

various  uses  of  the  term,  314. 
Alps,  geological  age  of,  294 
Alumina,  18. 
Aluminum,  nature  of,  18. 
Aluminous  Minerals,  characteristics  of,  19. 
Amber,  282. 

America,  S.,  elevation  of  the  coast  of,  123. 
Amethyst,  what  is,  19. 
Ammonite,  257. 
Amydaloid,  39. 
Anhydrous,  definition  of,  24. 
Animal  and  Vegetable  Life,  relations  of,  183. 

Kingdom,  divisions  of,  185. 
Animals,  distribution  of,  193. 

first  appearance  of,  208. 
recent  extinction  of,  315,  320. 
Anoplotherium,  288. 
Anthracite  Coal,  what  is,  245. 

where  found,  246. 
Anticlinals,  what  are,  77. 
Appalachian  Mountains,  height  of,  14. 

when  elevated,  248. 
Aqueous  Agencies,  133. 
Aqueous  Rocks  mechanically  formed,  47. 

of  chemical  origin,  51. 

of  organic  origin,  51. 

varieties  of  the,  47. 

Arctic  Regions,  ancient  temperature  of,  102. 
Argillaceous,  definition  of,  20. 

Slate,  62. 
Articulata,  varieties  of,  188. 

what  are,  188. 
Artesian  wells,  146. 
Ash  of  coal,  245. 
Asterolepis,  227. 

Atmosphere,  geological  action  of,  133. 
Atmospheric  Agencies,  133. 
Atols  of  the  Pacific,  164 
Augite,  what  is,  23. 
Australia,  Tertiary  fossils  of,  293. 
Axis,  anticlinal,  77. 
Azoic  Period,  178. 

scenery  of,  204 
.Azoic  Rocks,  203. 

Bad  Lands  of  Nebraska,  291,  292. 
Basalt,  what  is,  38. 

columnar  structure  of  89,  90. 


Beaches,  ancient  sea,  306. 

"       in  New  England,  306. 
Bee,  fossil,  282. 
Belemnite,  257. 

Birds,  extinct,  of  New  Zealand,  317. 
Birds'  tracks,  fossil  impressions  of,  265, 266. 
Bivalve  shells,  188. 
Bitumen,  246. 
Bog-Iron  Ore,  60. 
Bolca,  Mt.,  fossil  fishes  of,  284 
Bone  Caverns,  309. 
Borax,  where  found,  36. 
Bowlders,  what  are,  49. 

size  of  some,  298,  299. 

transportation  of,  298. 
Bowlder  formation,  296. 
Breccias,  50. 

Bricks,  red,  cause,  of  color  in,  23. 
Buhr  Stone,  what  is,  19. 

Caen  Stone,  253. 
Cainozoic  Period,  178,  275. 
Calcareous,  18,  20. 

tufa,  53. 

Calcium,  distribution  of,  18. 
Calciferous  sandrock,  212. 
California,  hot  springs  of,  119. 
Cambrian  System,  208. 
Cannel  (coal),  245. 
Carbon,  as  an  element,  17. 
Carboniferous  System,  229. 

divisions  of,  229. 

fossils  of,  229. 

vegetation  of,  235. 
Casts  of  fossils,  181. 
Catskill  Mountains,  geological  formation  of, 

Caverns,  ossiferous,  309. 
Central  heat,  100. 
Cephalopoda,  188. 

Chalk  and  Greensand,  origin  of,  270. 
what  is,  269. 
where  found,  269. 
Chlorine,  distribution  of,  17. 
Chlorite,  what  is,  23. 
Chloritic  Schists,  63. 

Classification  of  Rocks,  geological,  167,  173. 
Clay,  common,  composition  of,  19. 
Clay-Slate,  62. 
Clay-Stones,  what  are,  86. 
Cleavage,  origin  and  nature  of,  84,  85. 
Climate  of  the  Carboniferous  Epoch,  242. 
Clinkstone,  39. 

Clinometer,  use  of,  for  finding  dip,  76. 
Coal,  annual  production  of,  247. 

anthracite,  245. 

ash,  what  constitutes,  245. 

bituminous,  244. 

cannel,  what  is,  245. 


INDEX. 


329 


CoaL  distribution  of,  247. 

formation  of;  theory  of,  240. 

impurities  in,  245. 

magnitude  of  the  deposits  of,  240. 

plants,  fossil,  235-238. 

proof  of  the  vegetable  origin  of,  240. 

seams,  occurrence  of,  241,  243. 

spontaneous  combustion  of,  245. 

theory  of  the  formation  of,  244. 

varieties  of,  244. 
Comets,  density  of,  128,  129. 
Conchology,  denned,  188. 
Concretions,  origin  and  varieties  of,  86. 
Gonfervse,  what  are,  185. 
Conformability  of  strata,  77. 
Conglomerates,  what  are,  49. 
Connecticut  Valley  Sandstones,  fossils  of, 

265,  267. 

Coprolites,  what  are,  260. 
Coral  islands,  164 

reefs,  extent  of,  162. 
Corals,  formation  of,  162. 

of  the  Carboniferous  Epoch,  231. 
of  the  Silurian,  216. 
Contortions  of  strata,  79. 
Creation,  plan  of,  179. 
Cretaceous  Epoch,  life  of,  273. 

System,  269. 
Crinoids,  what  are,  233. 
Crustacea,  what  are,  189. 
Crust  of  the  earth,  what  is,  13. 

nature  of  the  original, 

199. 

thickness  of,  13. 
Cryptogamia,  what  are,  185. 
Ctenoids,  192. 

Cycadacese,  nature  of  the,  254. 
Cycloids,  192. 

Dead  sea,  depression  of,  16. 

Delta  of  the  Mississippi,  154,  313. 

Deltas,  what  are,  153. 

Devonian  System,  distribution,  divisions, 

and  fossils  of,  222-228. 
Diailage,  what  is,  40. 
Dikes,  rock,  what  are,  95. 
Diluvium,  48. 
Dinornis,  317. 
Dinotherium,  290. 
Diorite,  what  is,  38. 
Dip  of  strata,  75. 
Dodo,  extinction  of,  317. 
Dolerite,  what  is,  21,  66. 
Dolomite,  what  is,  38. 
Drift,  296. 

antiquity  of,  307. 

diffusion  of,  298. 

formation,  296. 

fossils  of,  308. 

glacial,  296. 

limits  of,  297. 

what  is,  43. 
Drift-formation,  296. 

theories  of,  304. 
Drift-strife,  301. 
Dunes,  or  Downs,  of  sand,  135. 

Earth  and  rocks,  non-conducting  properties 

of,  102. 
Earth,  axis  of,  possible  change  in,  11. 

change  in  the  temperature  of,  102. 

crust  of,  what  is  the,  13. 


Earth,  density,  12. 

elevation  and  depression  of  the  sur- 
face of,  121. 

excavations  in,  greatest  depth  of,  14. 
figure  of,  11. 

former  gaseous  condition  of,  130. 
heated  interior  of,  101. 
highest  mountains  of  the,  19. 
planetary  relations  of,  10. 
surface  configuration  of,  13. 
surface  of,  how  modified  by  igneous 

agencies,  121. 

temperature  of,  at  its  center,  100. 
thickness  of  the  crust  of,  13, 101. 
Earth's  surface,  area  of,  15. 
Earthquake,  definition  of  an,  114. 

motions,  114. 

Earthquakes,  duration  of,  115. 
frequency  of,  115. 
modern  (19th  century),  116. 
remarkable,  116. 
theory  of,  117. 
where  occur,  114. 
Echinoderms,  what  are,  190. 
Eggs,  gigantic  fossil,  319. 
Elements,  number  of,  16. 
Elephant,  fossil,  315. 
Elephants,  swamping  of,  316. 
Emmons'  Taconic  Theory,  206. 
Encrinites,  structure  of,  232. 
English  Channel,  how  formed,  166. 
Endogens,  plants,  184 
Eocene,  fossils  of  the,  284-287. 

Tertiaries,  279. 
Equisetacese,  185,  237. 
Erosion  by  water,  examples  of,  157-159. 
"Erratic  Block  Group,"  296. 
Eruptions,  volcanic,  phenomena  of,  107. 

remarkable,  110. 

Everglades  of  Florida,  formation  of,  165. 
Exogenous  plants,  184. 
Expansion  of  rocks  by  heat,  125. 

Fault,  defined,  82. 

Faults  and  dislocations,  82. 

in  the  Coal  Measures,  243. 
Feet,  impressions  of,  in  rock-strata,  267. 
Feldspar,  composition  of,  22. 
Ferns,  arborescent,  236. 
Fingal's  Cave,  91. 
Fire-clay,  what  is,  20. 
Fishes,  character  of  the  earliest  known,  225. 

classification  of,  187. 

forms  of  tails  of,  192. 

fossil,  classification  of,  190. 
Flexures  of  strata,  79. 
Flint,  what  is,  19. 
Flints,  gun,  87,  272. 

of  the  chalk-formation,  272. 
Foldings  of  strata,  79. 
Foliation,  85. 
Foraminifera,  271; 
Forests,  fossil  of  the  Oolite,  255. 
Formation  defined,  30. 
Fossil,  what  is  a,  28. 
Fossil  animals,  number  of,  196. 
Fossils,  different  forms  of,  181. 

general  characteristics  of,  180. 
the  oldest  known,  208. 
Freestone,  what  is,  50. 
Frost,  action  of,  on  rocks,  136. 
Fungi,  what  are,  185. 


330 


INDEX. 


Ganges,  sediment  transported  by,  154. 
Ganoids,  what  are,  191. 
Gas  springs,  14T. 
Gasteropoda,  188. 
Geodes,  what  are,  41. 
Geological  agencies,  98. 
periods,  ITT. 
Geology,  defined,  9. 

of  other  worlds,  131. 
of  the  moon,  131. 
and  religion,  324. 
Geysers  of  California,  119. 

of  Iceland,  119. 
Giant's  Causeway,  90. 
Glacial  epoch,  294. 
Glaciers,  what  are,  136. 

ancient,  in  New  England,  295. 
form  of,  136. 
geological  action  of,  142. 
motion  of  139. 
where  occur,  138. 
Globe,  changes  in  the  land-surface  of,  199. 

original  condition  of  the,  125. 
Gneiss,  defined,  64. 

geological  position  of,  204 
Gorges  and  canons,  152. 
Granite,  age  of,  200. 

composition  of,  42. 
definition  of,  41. 
geographical  distribution  of,  46. 
graphic,  43. 
origin  of,  44. 
varieties  of,  42. 
Graphite,  or  Plumbago,  246. 
Graptolites,  216. 
Grasses,  not  found  fossil,  282. 
Gravel,  what  is,  49. 
Greenland,  fossils  of,  102. 
Greensand  formation,  2TO,  2T1. 
Greenstone,  what  is,  38.    .. 
Guadaloupe,  fossil  man  of,  321. 
Gulf  States,  fossil  mammalia  of  the,  313. 
Gulf  stream,  158. 
Gypsum,  59. 

Hadrosaurus,  2T5. 
Hawaii,  great  volcano  of,  106. 
Herculaneum  and  Pompeii,  108. 
Heterocercal  tails,  192. 
Homocercal  tails,  192. 
Hornblende,  what  is,  23. 

schist,  63. 
Hornstone,  40. 

Horse,  fossil,  of  America,  293. 
Human  race,  antiquity  of,  320. 

fossil  remains  of,  321. 
Humus,  48. 

Huronian  System,  208. 
Button's  geological  views,  1T2. 
Hybrids,  what  are,  195. 
Hydrate,  what  is  a,  24. 
Hydrocarbons,  what  are,  244. 
Hydrogen,  distribution  of,  in  the  earth,  17. 
Hylseosaurus,  261. 
Hypersthene  rock,  38,  43. 
Hypozoic  rocks,  206. 

Ice  and  snow,  geological  action  of,  135. 
Icebergs,  how  formed,  142. 

size  of  some,  145. 

transporting  agency  of,  143, 144. 
Iceland,  volcanoes  of,  111. 


Ichthyosaurus,  258. 

Igneous  agencies,  99. 

Igneous  rocks,  relation  ofT  to  the  stratified, 

93. 

varieties  of,  31. 
Iguanadon,  261. 
Indusial  limestone,  285. 
Infusoria,  58. 

geological  action  of,  58. 
Infusorial  earth,  5T. 

in  Virginia,  58. 
Insects,  189. 

fossil  in  amber,  283. 

"    of  the  Oolite,  264. 
Interstratification,  25. 
Iron,  bog  ore  of,  60. 
hematite  ore,  8T. 
pyrites,  24 
sulphite  (sulphuret)  action  of,  on  coal, 

Jasper,  definition  of,  19. 
Jet,  what  is,  245. 
Joints  in  rocks,  81. 
Jurassic  System,  252. 

Kaolin,  46. 

Kilauea,  volcano  of,  described,  106. 

Kangaroos,  fossil,  293. 

Labyrinthodon,  the,  251. 

Lakes,  depression  of  the  beds  of,  15. 

Lamination  defined,  25. 

how  produced,  69. 

Land  and  sea,  changes  in  the  level  of,  122. 
Land   and  water,    distribution  of,  on  the 

globe,  16. 
Land-slides,  134 
Laurentian  Mountains,  206. 

System,  206. 
Lava,  33. 

Lavas,  varieties  of,  84. 
Lehman' s  geological  classification,  171. 
Leibnitz,  geological  views  of,  171. 
Lepidodendra,  nature  of,  237. 
Lias,  formation,  252. 
Lignite,  what  is,  255. 
Lime,  what  is,  18,  20. 

carbonate,  crystalline  forms  of,  21. 
how  detected,  21. 
in  water,  52. 
varieties  of,  20. 
Limestone,  what  is,  20. 
colors  of,  21. 
varieties  of,  20. 
Limestones,  fresh  water,  54. 

magnesian,  21,  56. 
marine,  55. 
metamorphic,  65. 
mountain,  229. 
Lithological  characters  of  rocks,  what  are, 

31. 

Loam,  what  is,  51. 
Lodes,  mineral,  84 

Madagascar,  extinct  birds  of,  319. 
Mammalia,  fossil  of  the  Tertiary  System, 

28T. 

orders  of,  187. 
Mammals,  reign  of,  287. 
Mammoth  and  mastodon,   differences  be- 
tween, 308. 


INDEX. 


331 


Mammoth,  great  fossil  of  Siberia,  308. 
remains  of,  in  England,  309. 
in  the  United  States,  315. 
Man,  fossil  remains  of,  321. 
geological  epoch  of,  320. 
last  of  Creation,  323. 
Manganese,  hydrate  of,  60. 
Marble,  definition  of,  20. 
Marl,  definition  of,  50. 
Marsupials,  characteristics  of  the,  252. 
fossil,  of  Australia,  293. 
what  are,  194. 
Mastodon,  epoch  of,  in  North  America,  315. 

largest  skeleton  of,  316. 
Megalonyx,  312. 
Megalosaurus,  261. 
Megatherium,  description  of,  311. 
Melaphyre,  40. 
Mesozoic  Period,  characteristics  of,  276. 

rocks,  ITS,  248. 
Metallic  veins,  84. 
Metals,  most  abundant,  18. 
Metamorpbic  rocks,  characteristics  of,  29. 
in  United  States,  165. 
Metamorphism  defined,  61. 
Meteorites,  origin  of,  181. 
Mica,  what  is,  22. 

schist  or  slate,  22. 
Mineralogy  defined,  10. 
Minerals,  calcareous,  what  are,  20. 
common,  24. 
siliceous,  what  are,  18. 
Mines,  deep,  temperature  of,  100. 

deepest  in  the  world,  14. 
Miocene  strata,  2T9,  280,  281. 
Mississippi,  bluffs  of  the,  314. 
delta  of,  154,  314. 
Missouri,  iron  mountain  of,  20T. 
Moa,  or  extinct  bird  of  New  Zealand,  318. 
Mollusca,  varieties  of,  187. 
Moon,  geology  of,  131. 
Moraines,  what  are,  140. 
Mosasaurus,  274 

Mountains,  highest  on  the  earth,  14. 
Mud-cracks  in  strata,  209. 
Mylodon,  312. 

Nebraska,  "  Mauvaises  Torres"  of,  291. 
Nebulae,  forms  of,  126. 

what  are,  125. 
Nebular  theory,  125, 126. 
New  Orleans,  geological  formation  of,  161. 
New  Red  Sandstone,  250. 
New  York,  fossil  corals  found  in,  216. 
New  Zealand,  animals  of,  293. 

extinct  birds  of,  317. 
Niagara,  geological  action  of,  151. 

geological  age  of,  308. 
Nodules,  what  are,  86,  87. 
Nomenclature,  geological,  principles  of,  178. 
Nummulites,  283. 
Nummulitic  limestone,  283. 

Obsidian,  34 

Ocean,  ancient  erosive  action  of,  159. 

depth  of,  15. 

eroding  power  of,  156. 
Oceanic  currents,  action  of,  156, 158. 
Oils,  natural  or  rock,  246. 
Old  Red  Sandstone,  description  of,  222. 
Olivine,  37. 
Oolite,  definition  of,  21. 


Oolitic  System,  252. 

Order  of  creation,  323. 

Organic  agencies,  160. 

Organization,  adaptation  of  condition  to,  192. 

Oriskany  sandstone,  223. 

Orthoceratites,  218. 

Ossiferous  caverns,  309. 

Outcrop  and  strike,  76. 

Oxyd  of  iron,  distribution  of,  23. 

Oxygen  in  rocks  and  minerals,  17. 

Pachydennata,  what  are,  283. 

fossil,  288. 
Palaeotheriuia,  288. 
Palaeozoic  Period,  178. 

rocks,  210. 

Palaeontology  defined,  10. 
Palisades  on  the  Hudson,  89. 
Palms,  fossil,  in  England,  281. 
Pampas  of  South  America,  formation  of,  311. 
Paris  basin,  fossils  of  the,  289. 
Peat,  160. 

relation  of,  to  coal,  244 
Periods,  geological,  178. 
Permian  System,  248. 
Petrifaction,  what  is,  182. 
Petroleum,  246. 
Petrology,  definition  of,  69. 
Phanerogamia,  184. 
Phosphorus,  in  rocks  and  minerals,  IT. 
Pitch  lake  of  Trinidad,  246. 
Pittsburg,  great  coal  seam  of,  240. 
Placoids  (fish),  191. 
Planets,  density  of,  129. 

geology  of  the,  131. 
Plants,  distribution  of,  193. 

of  the  Carboniferous  System,  235. 
varieties  of,  184. 
Plesiosaurus,  259. 

Pleistocene  era,  formations  of  the,  293. 
Pliocene  strata,  279. 
Plumbago  (Black-lead),  246. 
Plutonic  rocks,  32. 
Porphyry,  38. 
Post-Tertiary  Epoch,  313. 

formations  of,  313. 
economic  products  of,  822. 
Potassium,  as  a  constituent  of  rocks,  18. 
Potsdam  sandstone,  214. 
Prismatic  structurs  in  rocks,  89,  92. 
Protogene,  43. 
Protozoa,  190. 

Pterichthys,  or  winged  fish,  226. 
Pterodactyle,  description  of  the,  262. 
Pumice,  34. 

industrial  applications  of,  36. 
Pyramids,  stone  used  in  building  of,  283. 

Quartz,  definition  of,  18. 
crystals,  19. 
rock,  or  Quartzite,  22,  63. 

Radiata,  what  are,  189. 
Rain-drop  impressions,  fossil,  209. 
Rain-fall  of,  in  different  countries,  134 
Rain,  geological  action  of,  133. 
Recent  geological  formations,  314 
Red  River  raft,  160,  161. 
Reptiles,  age  of,  258. 

earliest  known,  227. 

of  the  Tertiary  System,  287. 

reign  of,  277. 


332 


INDEX. 


Richmond,  coal-fields,  near,  254 

Ripple-marks,  71. 

River-courses  and  valleys,  how  produced, 

152. 

drift,  illustrations  of,  161. 
Rivers,  geological  action  of,  149. 
traces  of  ancient,  SOT. 
sediment  brought  down  by,  153. 
terraces,  SOT. 
Rock,  definition  of  a,  16. 
Rocks,  aqueous,  2T,  30. 

chemical  composition  of,  16. 
chronological  classification  of,  175, 176. 
classes  of,  24. 

classification  of,  basis  for,  167. 
expansion  of,  by  heat,  125. 
fossiliferous,  28. 

"     estimated  thickness  of  the,  81. 
general  structure  and  relations  of,  69. 
granitic,  41. 
igneous,  2T,  30. 

"lost,"  of  the  Western  prairies,  303. 
metampTphjc,  29,  30,  61. 
minejFalogrcal  composition  of,  18. 
of  chemical  origin,  27. 
prismatic  structure  in,  89. 
specific  mineral  constituents  of,  21. 
gratified,  25. 

"       determination   of  the   age 

of,  16T. 
"       mechanical  displacement  of, 

74,  T5. 

trappean,  36. 
unstratified,  26. 
volcanic,  32. 

what  are  the  oldest,  199. 
Rocking-stones,  300. 
Rock-salt,  origin  and  distribution  of,  59. 
Rogers,  Prof.,  system  of  geological  nomen- 
clature, 249. 
Roman  cement,  88. 

Saliferous  rocks,  250. 
Salt,  rock,  59. 

lakes,  148. 

springs,  148. 
Sand,  common,  composition  of,  19. 

beaches,  origin  of,  135. 
Sand-dunes,  135.  - 

Sandstone,  what  is  a,  19,  50. 
Scaphite,  2T4. 
Schist,  51. 
Schistose,  51. 
Scorise,  what  is,  34. 
Sea,  depth  of,  15. 

beaches,  ancient,  305. 

water,  mineral  constituents  of,  57. 
Sediment  in  rivers,  153. 
Selenite,  59. 
Septaria,  what  are,  ST. 
Serpentine,  what  is,  23,  67. 
Siberia,  fossil  elephant  of,  309. 
Sigillaria,  238. 
Silica,  action  of  hot  water  on,  172, 173. 

principal  forms  of,  18. 
Silicates,  what  are,  19. 

artificial,  examples  of,  20. 
Silicious  rocks,  characteristics  of  the,  20. 

sinter,  57. 
Silicon,  17. 

Silurian  System,  characteristics  of,  210. 
fossils  of,  211. 


Silurian  System,  thickness  of,  22. 
Sivatherium,  291. 
Shale,  what  is,  51. 
Sharks,  fossil,  280. 
Sheep,  geological  age  of  the,  293. 
Shells,  varieties  of,  188. 
Silurian  System,  210-222. 
Slate,  what  is,  51. 
roofing,  208. 

Slickensides  defined,  83. 
Snow  and  ice,  geological  action  of,  135. 
Soil,  what  is  a,  48. 
Soils,  mineral  constituents  of,  48. 

organic  matter  in,  48. 
Solfataras,  what  are,  33. 
South  Carolina,  Eocene  fossils  of,  284. 
Spar  defined,  21. 
Species  defined,  195. 

extinction  of,  197. 
fossil,  number  of,  196. 
geographical  limitations  of,  194. 
animals  and  plants,  number  of,  195. 
propagation  of,  195, 196. 
Springs,  geological  action  of,  145. 

hot,  118.  . 

"     in  the  United  States, 
mineral,  147. 
,  origin  of,  145. 

saline  (salt)  148. 
Stalactites  and  stalagmites, 
Steatite,  what  is,  23.         jj 
Stone-lilies,  231.       .  ^     * 
Strata,  definition  of,  IB: 

disturbed,  contorted,  and  folded,  79. 
thickness  of,  how  determined,  81, 207. 
,.      when  conformable,  77. 

"      unconformable,  77. 
Stratification,  how  produced,  70. 
Stratified  rocks,  first  formed,  203. 
Stratum  defined,  25. 

of  invariable  temperature,  100. 
Structure  in  rocks,  31. 
Strike  (of  strata)  defined,  76. 
Sulphur,  natural  occurrence  of,  17,  36. 
Sweden,  subsidence  of  land  in,  122. 
Sypnite,  what  is,  42. 
Synclinal  axis,  what  is  a,  77. 
Systems  of  stratified  rocks,  enumeration  of 
the,  174. 

Taconic  System,  205.*" 
Talc,  what^s,  ,28* 
Talcose  schist,  63. 
Talus,  definition  of  a,  136. 
Teeth,  fossil,  of  sharks,  286. 
Temperature  of  the  earth,  100. 

mines  and  artesian  wells,  100. 
Terraces,  rivsr,  305,  307. 
Tertiary,  origin  of  the  name,  278. 

epoch,  physical  geography  of,  294. 
strata  in  America,  281. 
System,  278. 
Thallophytes,  185. 
Thermal  springs,  118. 
Tides,  geological  action  of  the.  156. 
Time  required  for  the  formation  of  strata, 

73. 

Trachyte,  34. 
Trap  rocks,  36. 

characteristics  of  the,  37. 
prismatic  structure  in,  89,  90. 
varieties  of,  38. 


INDEX. 


333 


Travertine,  53. 

Tree  ferns,  236. 

Trias,  250. 

Triassic  System,  250. 

Trilobites,  what  are,  214. 

Tufa,  calcareous,  53. 

Tuff,  or  Tufa,  definition  of,  34,  39. 

Turrilite,  274. 

Unconformable  strata,  77. 

United  States,  elevation  and  subsidence  of 

land  in,  123. 
volcanoes  in,  104. 
Univalve  shells,  188. 
Unstratified  rocks,  26. 
Upper  Silurian  rocks,  219.  . 

Valleys  of  erosion,  150. 
Vegetable  Kingdom,  classifications  of,  184 
life,  first  traces  upon  the  earth, 

208. 

life,  geological  influences  of,  160. 
Vegetation,  how  converted  into  coal,  224. 
Veins  of  igneous  rocks,  93,  95. 
injection,  93. 
segregation,  98. 

Vermont,  fossil  tropical  plants  found  in,  281. 
Vertebrate,  what  are,  186. 

animals,  classification  of,  186. 
Virginia,  Eastern,  coal-fields  of,  254,  255. 
Volcanic  action,  force  of,  112. 

districts,  surface  configuration  of, 


. 
glass,  34. 


35.          \ 

*? 


Volcanic  rocks,  32. 

rocks,  where  occur,  36. 
Volcano,  what  is  a,  32. 
Volcanoes,  craters  of,  106. 

eruptions  of,  107. 

extinct,  107,113. 

geographical  distribution  of,  106. 

in  the  moon,  132. 

mud,  109. 

number  of  active,  103. 

products  of,  35,  86. 

size  of  craters  of,  106. 

submarine,  33, 110. 

subterranean  connection  of,  113. 

Wad,  or  wadd,  60. 

Water,  erosive  power  of,  150. 

in  rocks  and  minerals,  24. 

power,  origin  and  source  of,  11. 
Watt's  (Gregory)  experiments  on  basalt,  92. 
Waves,  geological  action  of,  155. 
Wealden  formation,  262. 
fossils  of,  263. 
Wells,  Artesian,  146. 

temperature  of,  100. 
Werner's  classification  of  rocks,  173. 

geological  views,  171. 
Winds,  geological  action  of  the,  135. 
Winslow's  theory  of  earthquakes,  11& 
Worms,  a  class  of  articulata,  189. 

Zeuglodon,  289. 
Zoophytes,  what  are,  163. 


UNIVBEStTY 


PETRIFIED  FOREST. — The  San  Francisco  Alta 
offers  the  following  theory  as  to  the  formation  of 
the  famous  petrified  forest  near  Mount  St.  Helena, 
Cal.  :  During  one  of  the  periods  of  St.  Helena's 
volcanic  activity — we  assume  that  St.  Helena  was 
the  one — it  poured  out  a  great  abundance  of  ashes, 
some  of  which,  whether  dry  or  wet,  in  the  form  of 
mud,  filled  in  what  was  then  a  valley,  ten  miles 
southwest  of  the  summit  of  the  mountain.  This 
valley  has  its  redwood  trees,  which  are  buried  to 
a  distance  of  twenty  or  thirty  feet  above  their 
roots.  The  ash  or  mud  hardened  into  rock  ;  the 
trees  died,  and  the  tops,  exposed  to  the  air,  de- 
cayed away  and  disappeared.  The  buried  por- 
tions of  the  trunks  also  decayed  ;  but  as  they  did 
so  the  water,  trickling  down,  carried  with  it  sand 
and  soluble  minerals,  which  crystallized  in  the 

place  of  the  disappearing  fiber  until  the  vegetable 
had  been  replaced  by  a  mineral  trunk,  with  the 
form,  the  size,  the  structure,  the  vertical  grain, 
the  knots,  and  even  the  concentric  rings,  showing 
the  annual  growth  of  the  original  tree.  This 
petrifaction  was  harder  than  the  surrounding 
sandstone,  which,  in  the  course  of  centuries,  was 
washed  away,  leaving  the  stone  trees  standing, 
but  when  the  erosion  got  down  to  the  lower  end 
of  the  petrifactions  a  little  unevenness  in  the  sur- 
face deprived  the  trees  of  their  proper  support, 
and  they  fell,  breaking  into  short,-  transverse 
pieces,  as  we  now  see  them.  The  fracture  is  of  a 
kind  that  could  not  be  made  in  a  vegetable  fiber, 
and  that  we  should  find  very  difficult  to  make  in 
stone  while  lying  down  in  a  solid  surface.  The 
concussion  of  a  fall  of  a  brittle  material  explains 
it.  There  is,  we  believe,  no  known  instance  of 
petrifaction  in  open  water.  Petrifaction  requires 
decay  of  the  organic  material,  and  wood  is  pre- 
served, not  injured,  by  water.  The  condition 
most  favorable  for  petrifaction  is  an  inclosure  in 
a  sandstone  mold,  with  a  mild  temperature  favor- 
ins:  slow  decay,  an  outlet  through  the  sandstone 
for  the  decayed  material,  and  a  continuous  but 
slow  infiltration  of  a  fluid  saturated  with  lime 
or  other  crystallizing  minerals.  These  were  the 
conditions  at  the  Petrified  Forest. 


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